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The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Michael Christian Leitner 1,2, Frank Daumann 3, Florian Follert 4 & Fabio Richlan 1,2

1 Centre for Cognitive Neuroscience (CCNS), University of Salzburg, Austria

2 Department of Psychology, University of Salzburg, Austria

3 Faculty of Social and Behavioural Sciences, Friedrich-Schiller-University Jena, Germany

4 Faculty of Management, Seeburg Castle University, Austria

Draft version 1.1, 29/05/2021

This paper has not been peer reviewed yet.

Please do not copy or cite without author’s permission.

The authors declare that they have no conflict of interest.

Corresponding author: Michael C. Leitner / University of Salzburg / Centre for Cognitive Neuroscience / Department of Psychology / Hellbrunnerstrasse 34 / 5020 Salzburg / Austria [email protected] Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Abstract

Research question: The phenomenon of home advantage (or home bias) is well-analyzed in the scientific literature and is traditionally an interdisciplinary topic. So far, the phenomenon has been difficult to study because, although there have always been single matches where the spectators were excluded, this never happened globally to all teams within a league or even across leagues. Thus, several studies examined the influence of supporters by comparing matches before the COVID-19 restrictions with so-called ghost games during the pandemic.

Research method: To synthesize the existing knowledge after over a year of ghost games and to offer the scientific community and other stakeholders an overview regarding the numerous studies, we provide a systematic literature review that summarizes the main findings of 16 empirical studies and discusses the results accordingly.

Results: Our findings - based on 16 studies - indicate that ghost games have a considerable impact on the phenomenon of home advantage. No study found an increased home advantage in ghost games. Rather, our results show that 13 (from 16 included) analyzed studies conclude

– based on their individually examined data – a more or less significant decrease of home advantage in ghost games.

Implications: We conclude that our findings are highly relevant from a both socio-economic and behavioral perspective and highlight the indirect and direct influence of spectators and fans on football. Our results have – besides for the scientific community – a high importance for sports and team managers, media executives, fan representatives and other persons responsible.

Keywords: fans, home advantage, football, systematic literature review, COVID-19

2 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Introduction

Fans love football and especially the excitement and uncertainty of the game (Schreyer et al., 2018). They are also commonly referred to as the “12th man” (Saunders, 2020) and constitute an important part of the modern entertainment product “professional football” (Edensor, 2015). For the players, too, it obviously has a meaning whether they play in their home venue in front of their home crowd, on “their own corner” in the first or second half of a match, or on which goal the decisive penalty shootout in a play-off or cup competition takes place. From a scientific perspective, fans are seen as an (external) determinant in the production of sporting success and, consequently, of economic success (Dietl et al., 2005; Daumann, 2019).

It can hardly be denied that football benefits greatly from active spectators (Rudolph et al., 2017), whether through ticket revenues or through the typical stadium atmosphere that gives the product its special marketability (Woratschek et al., 2019). These benefits are also accompanied by (external) costs – such as violence (Di Domizio & Caruso, 2015; Dunning et al., 1986; Mause 2020) – posing considerable challenges for sporting and political players that regularly have to be borne by the clubs and the general public.

In the present review, we concentrate on the positive contribution of football fans and suggest interpreting fans as important production factors (Follert et al., 2020). In this context, the influence of fans on the game results mainly from the home advantage (Courney & Carron, 1992) (or home bias) which is well-documented in professional football and even reflected in the regulations of international competitions like UEFA Champions League1. The home advantage states that home teams win more than half of the games (excluding draws) when home and away games are evenly distributed in a season (Courney & Carron, 1992). Thus, a corresponding relative advantage of home teams over away teams can be assumed – albeit to varying degrees and based on different explanations (Buraimo et al., 2012; Courneya & Carron, 1992; Pollard, 2008; Ponzo & Scoppa, 2018; Schwartz & Barsky, 1977).

One factor that can be analyzed in the current COVID-19 situation, leading to almost laboratory-like conditions in stadiums, is the influence of (missing) fans on various social and sporting aspects during a football match (Bryson et al., 2020). In particular, the influences of the audience on the behavior and decisions of the referees (Dohmen & Sauermann, 2016) and

1 In case of a tie on points after two matches, a goal scored away from home counts double.

3 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective on the behavior and motivation of the players (Ponzo & Scoppa, 2018) can be specifically investigated.

After screening the broad relevant empirical literature as an outcome of the ghost games during the COVID-19 lockdowns, the additional benefit of another empirical study seems limited. For the international scientific community, it may be more important to bundle and synthesize the findings from this field. To this end, we provide a comprehensive overview of the empirical studies conducted so far during the match breakdown, the so-called “ghost games” period in the COVID-19 pandemic. These studies show that fans have to be considered as a significant production factor that can even influence the sporting outcome of a match. We aim to provide a comprehensive overview concerning the variety of empirical studies and to analyze their results from the view of behavioral economics.

The paper follows the following structure: In section 2, we provide a theoretical background for our literature review where we highlight the crucial findings concerning home advantages in sports as well as the important role of spectators for the production of a typical stadium atmosphere particularly in professional football. In section 3 we present the results of a systematic literature review that offers an overview on the relevant empirical studies to the scientific community and other stakeholders in the sports industry. Based on our findings we discuss the main results and the limitations of our study. In section 4 we present several implications for further research and sports business before we highlight some conclusions in section 5.

Theoretical background

Home advantage in professional sports. Following the seminal work by Courneya and Carron (1992) we understand a home advantage as “the consistent finding that home teams in sport competitions win over 50% of the games played under a balanced home and away schedule” (p. 13). First empirical evidence for the home advantage in sport competition was provided by Schwartz and Barsky (1977) who analyzed the major leagues in baseball, football, hockey, and basketball as well as the U.S. college competition in football and basketball. In the literature on sport psychology and sport economics, the home advantage effect is attributed to various influencing parameters, which Courneya and Carron (1992) systematize as follows:

● Game location factors (crowd, learning, travel, rules) ● Critical psychological states (competitors, coaches, officials)

4 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

● Critical behavioral states (competitors, coaches, officials) ● Performance outcomes (primary, secondary, tertiary)

The game location factors comprise four determinants that can affect the visiting and home teams differently. This includes the crowd factor (1.), according to which the home team receives greater support at home than the visiting team. Under learning/familiarity factors (2.) it is assumed that the home team is better acquainted with the location and also has the possibility to redesign it at short notice. In football, the watering of the lawn is likely to be relevant here as an example. Under the heading travel factors (3.) hides the fact that the visiting team has to travel to the venue and thus has to take on inconveniences to which the home team is not exposed. Finally, under rule factors (4.), components of the set of rules are subsumed that provide for favoring the home team. Carron et al. (2005) give the example of the last line change in ice hockey.

These four game location factors apparently affect directly the critical psychological states of the three relevant groups of actors and thus, indirectly their critical behavioral states. The three groups are the competitors, the coaches and the officials. The performance outcome is influenced by changing the critical psychological and behavioral states of the three groups. Coruneya and Carron (1992) differentiate between three levels: The primary level describes the basic level of performance (such as the distances covered in football or the number of sprints). The second level describes the intermediate or scoring aspect of the performance (e.g. the number of goals scored). The third level records the result measure (in football this would be the number of points that a team scores in a game).2

While, e.g., travel efforts for teams traveling to an away game have remained the same during the COVID-19 pandemic,3 crowd influence is of particular interest for our purposes. Relevant parameters that could have an impact on the outcome of (home) games are the crowd size or density (Dowie, 1982; Pollard, 1986). The structure of the stadium for the production of the atmosphere – e.g., standing room or steep stands – also seems to be a possible influencing factor (Fischer & Haucap, 2020).

2 A more recent summary of previous empirical research results on the home advantage can be found in Strauß & MacMahon (2020) and in Peeters & van Ours (2020).

3It could be argued that due to the numerous infection control regulations, travel and preparation for the game may be different and affect the teams. This is certainly true for both home and away teams, who may have to gather at a hotel for quarantine several days before a match.

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The role of fans in producing atmosphere and sporting success. Meanwhile, it seems largely uncontroversial that fans occupy a significant role in professional sports. In addition to their classic function as demanders and consumers of the entertainment service produced, however, they also play a role in other parts of the value creation process. Woratschek, Horbel and Popp (2014) describe the value contribution for the production as follows:

Perhaps most importantly, it must be considered that fans, who are also the customers, make an important contribution to sport events. This contribution often begins long before the event when they start coming up with battle chants and songs, preparing choreographies to be performed at the stadium or creating fan banners and posters. During the event, fans of the home and the away teams can contribute to the atmosphere in both positive and negative ways. Their participation in the value creation process continues after the sport event when they celebrate victories or jointly come to terms with losses. (p. 10)

The atmosphere within a stadium can be an important and beneficial factor for football fans (Flatau & Emrich, 2016). This finding is intuitive, however, the typical stadium atmosphere is an original output of the fans themselves. Following Endesor (2015) “atmosphere is ( ... ) a co- production that involves players, match organisers, and fans” (p. 82). Both sides contribute to the production of the game atmosphere through mutual interaction (Endesor, 2015). In Mauss' (1966) sense, the relation can even be interpreted as an exchange. From the player’s perspective the stadium represents a stage, similar to that of an actor in a theater. Basically, it is about the self-presentation of the players in public. The player needs the spectator, the big stage, to present himself and his performance (Gebauer, 1972; Goffman, 1959; Horky, 2020). The fans cheer on the team and in return the team fights on the pitch, so that the marketable entertainment service "football" is produced as a result. Giulianotti (2002) differentiates the heterogeneous group of spectators depending on the depth of their attachment to the clubs in supporters, fans, followers and flâneurs. Therefore, Giulianotti (2002) classifies spectators in four quadrants that are related to two binary oppositions: Hot-cool and traditional-consumer. Traditional (Taylor, 1971) spectators have a close connection to the club and are less market-oriented than consumers. The dimension hot means an emotional identification with the club. From a socioeconomic perspective, and as a classification for the purposes of our research question, which examines home advantage while spectators are away, it seems useful to consider the traditional-hot dimension, which is named as supporters by Guiulianotti (2015):

6 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Supporters habitually have a 'topophilic' relationship toward the club’s core spaces, primarily the home ground (Bale, 1994). Supporters attend regularly, coming to know the ground’s nooks and crannies in a very familiar, personal manner. The ground enhances their thick solidarity with fellow supporters, crowds of whom generate an atmosphere on match days that is considered to be special or unique. Supporting the club is a key preoccupation of the individual’s self, so that attending home fixtures is a routine that otherwise structures the supporter’s free time. Supporting the club is a lived experience, rooted in a grounded identity that is reflected in an affectionate relationship to the ground that is regularly revisited. Moreover, the supporter’s emotional investment in the club is reciprocated in several ways. (p. 33)

We are particularly interested in what happens when there are no spectators in the stadium, i.e. those supporters who are otherwise present through chants and cheers are also missing. There is a broad consensus regarding the anecdotal evidence that supporters as the "12th man" can also influence the outcome of the game, what is emphasized by Edensor (2015) from a sociological perspective:

Popular notions that supporters can affect the events that unfold during the game undergird the agency of fans in constituting a (good) atmosphere. Indeed, it is widely believed that the more fervent the support, the better will be the home team’s performance for they will be inspired by the levels of noise and excitement. Conversely, there is a possibility, it is advanced, that a hostile atmosphere will intimidate the away side. (p. 85)

COVID-19 and its influence on European football: A (quasi) natural experiment. Already in February and March 2020, numerous matches in European leagues were either cancelled altogether or played as ghost games. The European Football Championship was also canceled for summer 2020 and postponed to 2021 (Drewes et al., 2021). Due to the COVID-19 pandemic, games in the major European professional football leagues were suspended for the 2019/20 season in mid-March and then resumed in the form of ghost games in May and June 2020 (for an overview see Kicker, 2021).

In the English Premier League, the 2019/20 season was interrupted beginning with March 13, 2020. The season was concluded in the period from June 17 to July 26, 2020 with the exclusion of spectators. The 2019/21 season of the highest Spanish football league La Liga was officially

7 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective interrupted on March 12 and continued from June 11 to July 19, 2020 in the form of ghost games.

In the Italian highest professional football league, Serie A, the 2019/20 season was interrupted on March 9, 2020 and resumed on June 20, 2020 without spectators.

The 19/20 season of the highest French football league, Ligue 1, was completely canceled on March 13th, 2020. The championship title was awarded to first ranked team Paris Saint- Germain which was also the previous season’s champion. The 2020/21 season was resumed on August 21, 2020 in the form of ghost games.

In the highest German football league, 1. Bundesliga, the match between Borussia Moenchengladbach and 1. FC Cologne already took place as a ghost game on March 11, 2020 due to the COVID-19 pandemic. Finally, the 20/19 season was interrupted and resumed in the form of ghost games on May 15, 2020.

Also, in the international competitions organized by the UEFA, Champions League and Europa League, several games of the round of 16 were played as ghost games in March 2020 before both competitions were interrupted. In August 2020, games were resumed, but spectators were also excluded. Due to restrictions in several countries, both in terms of holding matches and allowing foreign teams to enter the country, some matches were even held at third-party locations, such as Budapest. At the moment (May 6, 2021), games in the major European professional football leagues are played in the form of ghost games, i.e., spectators are not allowed.

The following Table 1 offers a summarizing overview on European leagues in the COVID-19 pandemic. The peculiarity was that from a certain point on, most matches were played as ghost games, whereas in the pre-Covid 19 era ghost games were mostly punishments for clubs or their fans and thus mostly remained isolated events (Drewes et al., 2021). Generally, playing ghost games can be understood as a quasi-natural experiment, which makes it possible to examine the influence of the audience on various aspects of the match, especially its course and its outcome.

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Table 1. COVID-19 in European Leagues during 2020 (Drewes, Daumann & Follert 2021, 126 f.)

Date of Country League Proceedings Notes postponement

Austria tipico - Bundesliga March 18 Restart June 2 Ghost Games

Belgium Jupiler Pro League March 13 Season cancelled May 15 Club Brugge appointed Champion

Czechia Fortuna Liga March 12 Restart May 23 Ghost Games

Denmark 3F Superliga March 12 Restart May 23 Ghost Games

England Premier League March 12 Restart June 17 Ghost Games

Paris Saint Germain appointed France Ligue 1 March 13 Season cancelled April 30 Champion

Germany Bundesliga March 13 Restart May 16 Ghost Games

Italy Serie A March 9 Restart June 20 Ghost Games

Netherlands Eredivisie March 12 Season cancelled April 24 No champion appointed

Norway Eliteserien Season not started Restart June 16 Ghost Games

Poland PKO Ekstraklasa March 13 Restart May 29 Ghost Games

9 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Portugal Liga NOS March 12 Restart June 3 Ghost Games

Russia Premier Liga March 17 Restart June 19 Ghost Games

Scotland Scottish Premiership Season cancelled May 18 Celtic Glasgow appointed Champion

Spain La Liga March 12 Restart June 11 Ghost Games

Sweden Allsvenskan Season not started Restart June 14 Spectators allowed

Switzerland Raiffeisen Super League March 2 Restart June 19 Ghost Games

Turkey SPORTOTO SüperLig March 19 Restart June 12 Ghost Games

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Research design

Systematic literature review and literature identification process. The current COVID-19 pandemic has changed modern life in a substantial way, so it is not surprising that the sports sector – from children's gymnastics to the European Football Championship – is also affected by the government measures (Daumann 2020). Professional football is also feeling the (sports) economic impact; many clubs are facing financial challenges due to reduced revenues (Drewes et al., 2020; Drewes et al., 2021). As described above, the “ghost games” held since the spring of 2020 are of particular importance from a scientific point of view in that they represent a natural experiment in how changing framework conditions affect football, so that certain influences can be studied in isolation. It is therefore not surprising that numerous studies took up the topic after only a short time.

In order to provide a comprehensive overview of the empirical studies, their data, their methods and their findings, we analyze the field of study by means of a systematic literature review4. This approach is frequently used in psychology, in economics and in management research to present the state of the art in a certain field of research (Fisch & Block, 2018; Frank & Hatak, 2014; Webster & Watson, 2002).5

To cover the previous literature as comprehensively as possible, the databases EBSCO-Host, EconStor, SURF, Emeraldinsight, JSTOR, Sciencedirect, Springerlink and Google Scholar were searched on April 28, 2021 with the terms COVID-19, football, soccer, behind closed doors, ghost game, and home advantage. The following search strategies were used:

1. 'COVID-19' AND 'football' AND 'ghost game' 2. 'COVID-19' AND 'soccer' AND 'ghost game' 3. 'COVID-19' AND 'football' AND 'behind closed doors' 4. 'COVID-19' AND 'soccer' AND 'behind closed doors' 5. 'COVID-19' AND 'football' AND 'home advantage' 6. 'COVID-19' AND 'soccer' AND 'home advantage' 7. 'COVID-19' AND 'home advantage'

4 We follow Fisch and Block (2018) in their understanding of a systematic literature review in management research that this term “refers to all literature reviews that follow a systematic, transparent, and reproducible process for identifying academic literature about a clearly defined topic or research question”.

5 A related methodology is the bibliometric analysis in the form of content analysis, e.g., Mondello & Pedersen (2003).

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The keywords mentioned were only searched for in the titles of the articles. Newspaper articles and comments were excluded, so that in the end only articles from journals and working papers remained. Papers that were not relevant were also excluded. This was particularly the case with the EconStor and Springerlink databases. In this way, Table 2 shows the following results that could be obtained.

Table 2. Results of the database analysis (April 28, 2021). The number of contributions that are not relevant is given in parenthesis.

COVID- COVID- COVID- COVID- COVID- COVID- COVID- 19, 19, 19, 19, 19, 19, 19, Query football, soccer, football, soccer, football, soccer, home ghost ghost behind behind home home advan- games games closed closed advan- advan- tage Database doors doors tage tage

EBSCO_HOST 1 1 0 0 0 1 2

EconStor 2 2 (1) 1 1 3 3 (1) 11 (6)

Emeraldinsight 0 0 0 0 0 0 0

Google 0 1 0 0 5 2 13 (1) Scholar

JSTOR 0 0 0 0 0 0 0

Sciencedirect 0 0 0 0 0 0 0

Springerlink 0 0 7(7) 2 (2) 0 0 0

SURF 0 0 0 0 0 0 0

Additionally, to this structured search, we manually worked through the references of these papers to find papers that had been overlooked. One study provided only descriptive data because the focus was not on home advantage, and one paper was published in a journal whose doi was not accessible. After we removed duplicates, 16 papers (10 peer-reviewed) from 2020 and 2021 remained that formed our sample to be analyzed.

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Study characteristics. After identifying eligible studies – as described in the previous section – we studied the included manuscripts in more detail. Besides basic properties and information (year, authorship, journal, peer-review status, etc.) the following characteristics were extracted and documented in detail: number of reported countries, number of analyzed leagues, method of comparison (within or between leagues), number of focussed seasons, number and properties of analyzed factors (e.g., goals, cards, fouls, etc.), number and properties of used statistics, results and (central) conclusion.

To measure the scientific quality of our sample at least heuristically, we created an individual “Quality Score” for every study – used as a proxy that allows a comparison between the respective studies in terms of such as breadth and depth of analysis, methodological design, statistics used and factors included – we quantified the studies’ crucial components “Leagues”, “Leagues comparison”, “Seasons”, “Main factors”, “Side factors” and “Statistics”. In order to achieve a final score for each work the studies were analyzed individually for similarities and differences in their analytical approach, and weightings were used respectively to provide a balanced assessment of the included characteristics. The weighting was based on calculated mean values across all studies. This approach prevented individual study characteristics from having a biasing influence on the respective overall picture, represented in the concluding “Study quality score” and were calculated as follows.

A. “Leagues”: The sum of all 1st leagues (0.5 points per league), 2nd leagues (0.25 points per league) and 3rd leagues (0.1 points per league) were calculated. When the “Top 4 Leagues” (England, Spain, Italy, Germany) were included into the study 5 bonus points were added. The final score resulted in the “Combined leagues subscore”. B. “League comparison”: 0 points were awarded to studies calculating within or between different leagues, 2.5 points were awarded to studies calculating within and between different leagues. C. “Seasons”: The number of included seasons was weighted with a score of 0.5. D. “Main factors” & “Side factors”: After analyzing every study, we identified and extracted 4 main factors on home advantage (win ratio or points, goals, cards and (regular) attendance). Following the same logic, we further found several side factors on home advantage (e.g., shots, fouls, corners, possession, etc.). We awarded 1 point for every main factor and 0.25 points for every side factor included into the study, culminating into a “Analyzed factors subscore”.

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E. “Statistics”: We identified 3 principal statistical approaches to investigate the home advantage in ghost games. Those were correlations, regression, and stochastics. We awarded 2.5 points for each approach.

The sum of the individual values from the list from A to E forms the "Study quality score" and thus reflects a concise comparative value between the different studies.

Besides calculating an individual “Study quality score” for every study we additionally set another individual value – the “Study conclusion score” – representing the central conclusion of each study in terms of the magnitude of the impact of ghost games on home advantage. In order to set this score, we screened every paper for crucial text passages indicating the authors verdict on the home advantage in ghost games, based on their findings. A 7-point non-directed likert scale (ranging from (1) “strongly increased home advantage in ghost games” to (4) “no change in home advantage in ghost games” and (7) “strongly reduced home advantage in ghost games”) was used to represent the studies’ conclusion as precisely as possible.

Summing up, we assigned two values to every included study, the “Study quality score” and the “Study conclusion score”. While the "Study quality score" represents a central statement regarding the depth, breadth, and empirical significance of the respective study, the "Study conclusion score" reflects the central statement of the authors regarding the influence of ghost games on the home advantage.

Results

Analyzing all included 16 studies (10 peer-reviewed), the “Study quality score” mean value is 17.1 (SD = 5.2) and the “Study conclusion score” is 5.8 (SD = 1.2), as illustrated in Figure 1.

When applying more “strict methodological and empirical standards” to the studies – that is only including peer-reviewed studies and studies investigating more than one league (inclusive the “Top 4 European leagues”) – seven studies with a “Study quality score” mean of 20.6 (SD = 3.1) and “Study conclusion score” mean of 5.9 (SD = 1.2) remain, as illustrated in Figure 2.

Following, the central conclusions and respective crucial text passages from each of the 16 included studies – that led predominantly to the “Study conclusion score” – are presented in more detail in Table 3.

14 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Figure 1. Results illustrating the individual “Study quality score” (left y-axis and blue bars) with a mean of 17.1 (SD = 5.2) – illustrated by the green bar – and the individual “Study conclusion score” (right y- axis and orange line) with a mean of 5.8 (SD = 1.2) – illustrated by the green dot – of all 16 included studies (x-axis) investigating the effect of ghost games on home advantage (HA) in football. Peer- reviewed studies are marked with an asterisk. The “Study conclusion score” on the right y-axis ranges from 1 to 7, representing the following: 1: strongly increased HA / 2: increased HA / 3: slightly increased HA / 4: no change in HA / 5: slightly decreased HA / 6: decreased HA / 7: strongly decreased HA. The “Study quality score” on the left y-axis represents a value formed by different subscales (see previous section for details), allowing a quantified comparison between the studies included regarding breadth of analysis, methodological design, statistics used and factors included.

15 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Figure 2. Results illustrating the individual “Study quality score” (left y-axis and blue bars) with a mean of 20.6 (SD = 3.1) – illustrated by the green bar – and the individual “Study conclusion score” (right y- axis and orange line) with a mean of 5.9 (SD = 1.2) – illustrated by the green dot – of both peer-reviewed and multi-leagues studies (x-axis) investigating the effect of ghost games on home advantage (HA) in football. The “Study conclusion score” on the right y-axis ranges from 1 to 7, representing the following: 1: strongly increased HA / 2: increased HA / 3: slightly increased HA / 4: no change in HA / 5: slightly decreased HA / 6: decreased HA / 7: strongly decreased HA. The “Study quality score” on the left y-axis represents a value formed by different subscales (see previous section for details), allowing a quantified comparison between the studies included regarding breadth of analysis, methodological design, statistics used and factors included.

Table 3: Listing of key findings from the included studies on the relationship between ghost games and home advantage. Interpretation led to the “Study conclusion score”, illustrated in Figure 2 and 3.

Study Page Quote (First author, year)

Bryson 2021 1 "We find large and statistically significant effects on the number of yellow cards issued by referees. Without a crowd, fewer cards were awarded to the away teams, reducing home advantage. These results have implications for the influence of social pressure and crowds on the neutrality of decisions."

16 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Scoppa 2021 1 "The evidence we provide strongly supports the idea that social pressure has intense effects on agents’ behavior."

Konaka 2021 9 "More simply, the home advantage became smaller when the games were conducted behind closed doors."

Sánchez 2021 152 "The results show that there are no significant differences between playing with or without a crowd, except in the German and Spanish top leagues. Even so, there is a tendency in most competitions to play worse at home and better away from home when there are no spectators."

Wunderlich 2021 1 "The present data is evidence that in absence of spectators the increased sanctioning of away teams disappears, the match dominance of home teams remains, but is decreased and the home advantage itself decreases, yet insignificantly." Benz 2020 16 "In some leagues, evidence is overwhelming that HA declined for both yellow cards and goals. Alternatively, other leagues suggest the opposite, with some evidence that HA increased." McCarrick 2020 N/A "Our data thus support a wealth of previous literature showing that the presence of a crowd can have a strong effect on home team performance." (Discussion section; lines: 392-393) / "We suggest that the unique circumstance provided by the Covid-19 pandemic has demonstrated that a key element of the HA (the crowd influencing players and referees) has been confirmed." (Discussion section; lines: 420-422 )

Almeida 2021 693 "Overall, the HA did not significantly decrease in European leagues (from 16.4% to 11.6%; trivial effect size [ES]); however, a one-sample t-test revealed that the HA after the COVID-19 break was significantly greater than 0% (small ES)." Hill 2021 1 "We conclude that the home field advantage may indeed be lost when spectators are absent."

Sors 2020 1 "The results bring further support to the claim that, among all the factors contributing to home advantage and referee bias, crowd noise has a relevant role. Thus, spectators can significantly contribute to determine the dynamics and the outcomes of professional football matches."

17 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Leitner 2021 16 "We conclude that due to the missing supporters in games of professional elite football during the COVID-19 pandemic, referees perceived less social pressure from the home crowd, leading to the dissolvement of the home advantage effect." Fischer 2020 0 "We find that there is a reduced home advantage in the first division, whereas no change is observed in the second and third division." / "We cannot find strong evidence for a change in referee behavior or teams' tactics as main impact channels of occupancy rates on the home advantage. We rather assess psychological reasons to be of higher importance."

Dilger 2020 I "Comparing these games ["ghost games"] with the regular ones between the same teams before, we find that the normal advantage for the home team disappears. One reason for this is the disappearances of the home bias of the referees whereas changes in the sportive performance of the teams seem to be irrelevant in this regard."

Santana 2021 1 / 5 "The return to football pitch without stadium supporters, affected some game and physical variables, as well as home advantage." / "Although, a high number of match variables were slightly favorable to home teams, their home advantage was lost." Matos 2021 1 "Overall, despite what might be expectable from recent findings, the lack of an audience in the last 10 rounds of Portuguese Football League 2019–2020 season, due to COVID-19 pandemic, did not affect home advantage."

Tilp 2020 1 "[...] the Covid-19 lock-down led to a home disadvantage. One reason for this surprising result could be that the home team is missing an important familiar aspect when playing in their empty stadium without social support from their home audience. Furthermore, both teams know about the HA thus the away team could be more motivated in this unusual situation."

Discussion and implications

Main results. Based on our findings, we conclude the following: According to current empirical studies, the role of fans seems to be significant for the outcome of matches in professional football. The results from our review on 16 studies on home advantage in ghost

18 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective games further indicate that the home advantage indeed decreases considerably during ghost games. There is not a single study that found an increased home advantage in ghost games: three studies conclude “no change in home advantage”, three studies conclude a “slightly reduced home advantage”, four studies conclude a “reduced home advantage” and six studies conclude a “strongly reduced home advantage” in ghost games. When analyzing only peer- reviewed and studies that included the top four leagues (England, Spain, Italy, Germany) the overall conclusion distribution is similar: from seven studies, one study concludes “no change in home advantage”, two studies conclude a “slightly reduced home advantage”, one study concludes a “reduced home advantage” and three studies conclude a “strongly reduced home advantage” in “ghost games”. In this respect, the results of the examined papers, which worked with primary data, support the theory that fans have a significant impact on home advantage in professional football.

With regard to the existing explanatory approaches in the literature, the theory of social pressure seems to emerge as an empirically conclusive explanatory model for the found effect of decreased home advantage in ghost games. Most studies suggest that a relationship between spectator absence and home advantage can be inferred via the influence on the referee(s). Although a less emotional behavior (e.g., Webb 2020), especially a lower level of aggression towards referees, may be desirable from a sporting perspective, it seems to come at the expense of the home advantage and is reflected in a lower sporting success of the home team.

Implications for football clubs and organizers. The question now arises as to what implications the empirical evidence might have with regard to the club’s governance. In the sports economics literature, it has been discussed for several years to explicitly consider fans in the club's objective function ("fan welfare maximization", e.g., Madden 2012; Madden and Robinson 2012). Although this demand may be criticized with reference to the importance of ownership in a market economy system and the advantages of having an investor as “sugar daddy” (see Franck 2010; Rohde and Breuer 2016; Richau et al. 2021), it is worth considering compensation for fans for providing the factor of production (see Follert, Daumann, Passon 2020). That fans also hold a majority stake in a football club is not unheard of. For example, the Exeter Supporter's Trust holds a majority stake in Exeter City FC, which plays in the English League Two (4th division). Although the supporters achieve a consumption benefit from that football match as it is, there is already reciprocity here in that they pay the admission price for this. The bargaining position of the fans is certainly strengthened by the empirical data provided

19 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective by the studies that we found in our review, so that they could possibly demand greater influence on strategic and operational club decisions. However, it must be considered that fans have strongly limited alternatives for time allocation, provided that they want to spend their free time-consuming football. It is easy to see that a fan of FC Bayern Munich will not switch to Borussia Dortmund if "his” or “her" club denies him or her recognition. Thus, due to their preference structure, fans suffer considerable utility losses when choosing the option "migration".6 We can conclude that the stronger the bond between club and fan, the harder the exit will be, since the alternative provides only a comparatively small benefit. With respect to the differentiation provided by Giulianotti (2002), a spectator who is classified as hot and traditional will almost never switch to another club. This does not mean, of course, that the clubs can act without paying any attention to the fans. Rather, it seems necessary for clubs to produce a minimum level of sporting success in order to “keep fans in line” in the medium and long term, which in turn has corresponding implications for sports management (signing of players, ticket pricing, etc.).

Besides that, the market power of the fans must not be overestimated from a different perspective: The market power of the fans essentially depends on their level of organization. If the fans can confront the clubs as a closed cartel, they are certainly able to assert their interests. Social media enable such an organization and reduce the corresponding communication costs, but on the one hand the number of fans is very high and on the other hand their interests are often very differentiated. Thus, an appearance of the fans as a closed cartel seems rather unlikely, which means that the price-setting scope of the clubs should remain comparatively high.

However, the role of fans can also be used for strategic purposes. It can be interesting for the organizer of national as well as international competitions to choose the venue in such a way that the role of the fans is marginalized, and the "actual" athletic performance of the opponents dominates the result of the game. At the same time, it should be noted that this can of course also have effects on the other sub-markets such as the market for sponsoring, TV broadcasting rights and merchandising.

It could also be interesting for the visiting team to purchase tickets for away games and distribute them free of charge to their own fans, in the hope that this subsidy will increase the

6 See Hirschman (1970).

20 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective number of their own fans in the away game and thus at least partially eliminate the home advantage.

Implications for further research. In line with the classical conceptual framework for research on home advantage (Courneya & Carron, 1992), we found strong evidence for the crowd as a crucial game location factor. In our systematic review the effect of the missing supporters was not only evident with respect to performance and outcome measures (i.e., win ratio, points, goals), but also in measures more directly related to the critical behavioral states of players and referees, such as match dominance (i.e., shots, shots on target), fouls, and cards.

From a behavioral science perspective, the consequent relevant question would be about the underlying psychological states of the players and referees. At the moment, the relationship between behavioral and psychological states can only be indirectly inferred from the present data (Webb, 2020). Anecdotal evidence from interviews with players (Guardian Football, 2020; Hamilton, 2021) and referees (UEFA.tv, 2020; ZDFsport, 2020), however, indicates a substantial impact of the missing supporters on the subjective experience of these sports professionals.

Besides qualitative interviews and self-report questionnaires, a promising approach was recently put forward by Leitner & Richlan (2021b). Their “Analysis System for Emotional Behavior in Football“ (ASEB-F) is a video-based categorical analysis system of nonverbal behavior during football matches. It assumes that emotions can be observed and described as an organized psychophysiological reaction to specific events in the environment, rising to overt actions and leading to human (nonverbal) behavior. The ASEB-F was used to video analyze the behavior of players and officials in 20 games of FC Red Bull Salzburg before and during the COVID-19 pandemic. There were about 20% fewer emotional situations in matches without supporters compared to matches with supporters. In addition, referees were markedly less actively involved in these emotional situations. The results indicate that the absence of supporters has a substantial influence on the experience and behavior of players and officials alike.

Possibly related to the psychological effects is the question of whether there are particularly home strong or home weak teams, and, if yes, what the underlying mechanisms are. In addition, our systematic literature review revealed studies which reported differences in the effect of the missing supporters on the home advantage between leagues within counties (e.g., first vs.

21 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective second divisions) and differences between leagues across countries (e.g., German Bundesliga vs. English Premier League). Therefore, not only psychological but also socio-cultural explanations for the effects in question have to be taken into account.

In summary, pending questions for future research on the home advantage in football concern (among others) are: a) the psychological basis of the behavioral effects, b) differences between teams within leagues, c) differences between leagues within countries, d) differences between leagues across countries, and e) the effects of partial attendance (i.e., only a limited number of - primarily - home fans allowed in the stadiums as a measure of normalization after the COVID- 19 pandemic) on the home advantage.

Limitations. When analyzing the data and interpreting the conclusions of the individual studies, the question of a potential “publication bias” (sometimes also referred to as “file-drawer problem”) came up when looking at the results of our review. Our analyses show that none of the 16 – in some cases significantly different – studies included was able to find an increase in home advantage during ghost games. Likewise, the strong clustering in categories 6 & 7 (decreased & strongly decreased home advantage) of the "Study conclusion score" is striking. In a similar vein, only 3 of 16 studies concluded that the home advantage did not change significantly as a result of the ghost games in European football. In the light of these findings it is quite possible that the ghost games might indeed have brought a significant reduction in home advantage. Nevertheless, the possibility must be considered that results from other studies – that were not published due to “scientifically unpopular results” – would potentially weaken the effect of significantly reduced home advantage during the COVID-19 related ghost games in our review study.

Another key issue to consider when addressing the question of the impact of ghost games on home advantage is how to operationalize home advantage. In this context, different approaches and various constructs can be found in the scientific literature. While some studies choose the win-ratio or gained/lost points to represent home advantage, other study authors decided to rather analyze the distribution of by the referee awarded yellow and red cards to the home and away teams. There is also the empirical approach to analyze match specific aspects, such as “match dominance” (e.g., characterised by ball possession, shots on target or successful tackles) or other sport-performance related characteristics. Especially in a review study, this divergent approach creates potential problems in an inferential statement. However, our present paper does not attempt to make a judgement on these different approaches. Rather, we argue that these

22 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective circumstances need to be taken into account in a final evaluation, but that at the same time it does justice to a broad overall picture of the influence of “ghost games” on home advantage in professional football.

We decided to classify the literature using a metric to provide the scientific community with a tool to evaluate the results. However, we must point out that this can only be an approximation at best. In particular, the score is not intended to evaluate the authors behind it.

Conclusions

At first glance, one might think that the observed effect is equalized within a season if all matches are played under the same conditions, i.e., as ghost games. However, this seems to fall short for two major reasons. On the one hand, home advantage is not expected to decline in the same way for all teams. For example, since the studies only looked at aggregated data, it is still completely unclear whether fans' specific attachment to their team influences the strength of the home advantage or its decline. On the other hand, due to the legal framework in a federal system, such as in Germany for example, the conditions within a season do not necessarily have to be the same for all teams. For example, there may be cities that still allow matches with few spectators, while restrictive cities go straight to ghost games.

The COVID-19 pandemic is one of the most drastic crises since the last world war and affects all areas of society, including sports in general and professional football in particular. From the perspective of economic football research, this gives rise to numerous questions that are of both practical and scientific interest. In addition to economic issues, such as the viability of clubs without spectator revenues, the changed stadium atmosphere is particularly striking. Already at the beginning of the pandemic, there was anecdotal evidence that the behavior of players changed, e.g., toward referees, and recent studies indicate that the missing crowd indeed has an impact on the (nonverbal) behavior of players, staff and referees (Leitner & Richlan, 2021b). Since games without spectators were played in almost all European leagues from mid-2020 at the latest, the situation could be compared with a natural experiment. To this respect, our paper focuses on the importance of football fans, who face the restrictions in the pandemic of so- called “ghost games”. For this purpose, our paper presents a systematic literature review of the variety of empirical studies, which analyzes the quasi-experimental situation and finds evidence for a decrease in home advantage in most leagues. Apart from reviewing the main results of the

23 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective papers we provide a detailed analysis of study characteristics. For this purpose, we develop a new metric which can help to approximate the studies’ qualities.

Our findings suggest that, from a wide variety of perspectives - whether (socio)economic, psychological, or sports science - the highest premise should be to allow spectators and fans back into the world's stadiums as soon as the epidemiological conditions of the COVID-19 pandemic allow.

Acknowledgment

We would like to thank the participants of the 24th Annual Meeting of the German Association of Sport Economics and Sport Management for their valuable comments on this project.

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References marked with an asterisk indicate studies included in the systematic review

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33 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Appendices

Table 4: Listing of analyzed details of all included studies investigating the relationship between ghost games and home advantage.

Analyzed Analyzed Journal; Analyzed Nr of Year / Nr of Nr of League games games Analyzed Platform / Title Objectives leagues and analyzed Statistics Authors countries leagues comparison (Pre- (During- factors Status (Tiers) seasons Covid) Covid) Germany (1, 2); Denmark (1); Austria Estimating (1); Portugal the change in (1); Greece soccer's home Showing (1); Spain advantage validity of (1, 2); 2020 / arXiv / not during the Poisson Turkey (1); 5 (2015 - Regression Benz LS; peer-reviewed Covid-19 regression in 13 17 Individual 25.158 1699 Goals; Cards Sweden (1); 2019) analysis Lopez MJ yet pandemic analysis of Norway (1); using home England (1, bivariate advantage 2); Italy (1, Poisson 2); regression Switzerland (1); Russia (1) Win ratio; points; goals; Investigation market value; of changes in extra time; 2020 / Econstor / not No home bias Correlations; home shots; distance Dilger A; peer-reviewed in ghost 1 1 Germany (1) N/A 1 (2019) 223 83 Regression advantage covered; passes; Vischer L yet games analysis during "ghost possession; games" tackles; fouls; yellow cards; red cards

34 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Win ratio; points; player value; table position; pause Does Crowd (from last Support match); shape Drive the (points earned Home Analysis of in last three CESIfO Advantage in relation matches); travel 2020 / Working Professional between Correlations; Germany (1, 3 (2017 - distance; Fischer K; Papers / not Soccer? crowd 1 3 Individual 2702 274 Regression 2, 3) 2019) altitude; new Haucap J peer-reviewed Evidence support and analysis coach; yet from German home matchday; Ghost Games advantage daytime; derby; during the stadium track, COVID-19 share standing Pandemic places, capacity; yellow cards, fouls; shots; corners

Comparison of home 2021 / Home- advantage in International Matos R; Advantage last ten Journal of Monteiro during rounds Correlations; Environmental D; Antunes COVID-19: ("ghost 4 (2016 - Regression Research and 1 1 Portugal (1) N/A 1134 90 Points R; Mendes An Analysis games") with 2019) analysis Public Health D; Botas J; in Portuguese 24 rounds (ANOVA) / peer- Clemente Football before in reviewed J; Amaro N League same season and seasons before

35 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

England (1, 2); Germany (1, 2); Spain Home (1, 2); Italy advantage 2020 / Home crowd (1, 2); during the McCarrick causes the Portugal (1); PsyArXiv / Covid-19 Points; Goals; D; Bilalic referee to Greece (1); Regression not peer- pandemic: 11 15 Across 1 (2019) 6976 2552 Fouls; Cards; M; Neave unconsciously Turkey (1); analysis reviewed yet analyses of Corners; Shots N; Wolfson favor the Austria (1); European S home team Denmark soccer (1); Russia leagues (1); Switzerland (1) The sound of silence in Win ratio; association Effect of Points; Goals; football: 2020 / Sors European missing Germany (1, Ball possession; Home F; Grassi Journal of crowd noise 2); England Shots; Shots on advantage 4 (2016 - M; Sport Science on home 4 8 (1, 2); Spain Across 9564 841 target; Corner Correlations and referee 2019) Agostini T; / peer- advantage (1, 2); Italy kicks; Fouls; bias decrease Murgia M reviewed and referee (1, 2) Cards; Penalty in matches bias kicks; Extra played time without spectators Hypothesis of Covid-19 Has decrease in Turned Home home frontiers in Advantage advantage 2020 / Tilp Sports and Into Home and a more Win ratio; 2 (2018 - M; Thaller Active Living Disadvantage balanced 1 1 Germany (1) N/A 529 83 Fouls; Cards; Correlations 2019) S / peer- in the distribution of Penalty kicks reviewed German fouls and Soccer disciplinary Bundesliga cards in ghost games

36 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Professional football in times of Points; Goals; COVID-19: Change of Germany 2021 / Shots; Biology of did the home home (1); Spain Almeida Across & Possession; Sport / peer- advantage advantage in 5 5 (1); England 1 (2019) 491 491 Correlations CH; Leite Individual Passes; Aerial reviewed effect European top (1); Portugal WS Duels; Tackles; disappear in leagues (1); Italy (1) Cards European domestic leagues? Albania (1); Australia (1); Austria (1, 2); Costa Rica (1); Denmark Causal effects (1); England 2021 / Effect of of an absent (1, 2); Bryson A; missing social crowd on Germany (1, Dolton P; pressure on Economics performances 2, 3); Greece Win ratio; Reade JJ; players and Across & Regression Letters / peer- and 17 23 (1); Hungary 1 (2019) 4983 1498 Attendance; Schreyer referees in Individual analysis reviewed refereeing (1); Italy (1, Goals, Cards D; professional decisions 2); Poland Singleton football during Covid- (1); Portugal C matches 19 (1); Romania (1); Serbia (1); Slovenia (1); Spain (1, 2); Ukraine (1)

37 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Creating a large dataset Losing the of 1,000,000 Home Field randomized Advantage samples in When order to test Germany Points; goals; 2021 / Hill frontiers in Playing the (1); Spain Across & 5 (2015 - shots; Y; Yperen Psychology / Behind 4 4 5784 416 Stochastics hypothesis (1); England Individual 2019) possession; N peer-reviewed Closed Doors that the (1); Italy (1) fouls; cards During abscence of a COVID-19: home crowd Change or changes the Chance? home field advantage

Home advantage of England (1); European arXiv / not Evaluation of Germany Correlations; 2021 / major Across & 10 (2010 Win ratio; peer-reviewed "crowd 4 4 (1); Italy 17.729 430 Regression Konaka E football Individual - 2019) Goals yet effects" (1); Spain analysis leagues under (1) COVID-19 pandemic No more advantage for Effect of Spain (1); the home missing England (1); team: supporters on Germany 2021a / Refereeing decisions by PsyArXiv / (1); Italy Leitner without social referees in 2 (2018 - Win ratio; not peer- 8 8 (1); Russia Across 645 641 Correlations MC; pressure in "ghost 2019) Fouls; Cards reviewed yet (1); Turkey Richlan F European games" (1); Austria elite football during the (1); Czech during the COVID-19 Republic (1) COVID-19 pandemic pandemic

38 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

Analysis of Points; Goals; home Table position; advantage Stadium Home Germany (1, based on performance; 2021 / advantage in 2); Spain (1, Soccer & wins, points Number of Correlations; Sánchez European 2); Italy (1, Across & Society / peer- and goals, 5 8 1 (2019) 3981 1589 foreigners; Regression AJ; Lavín soccer 2); England Individual reviewed budget and Players' analysis JM without (1); Austria average experience; crowd (1) attendance Cards; Budget; during ghost Average games attendance Win ratio; Goals; Goal attempts; An analysis Analysis of Possession; 2021 / of Bundesliga missing Passes; Passes Science and Correlations; Santana H; matches crowd on accuracy; Medicine in Regression Bettega O; before and game 1 1 Germany (1) N/A 1 (2019) 224 81 Tackles; Football / analysis Dellagrana after social statistics and Corners; peer-reviewed (ANOVA) R distancing by home Offside; Fouls; COVID-19 advantage Team distance covered; Number of sprints Social Effect of pressure in missing social Germany (1, the stadiums: Points; Goals; Journal of pressure on 2); England Do agents Shots; Shots on Correlations; 2021 / Economic players and (1, 2); Spain 10 (2010 change 5 9 Across 33957 917 target; Corners; Regression Scoppa V Psychology / referees in (1, 2); Italy - 2019) behavior Fouls; Cards; analysis peer-reviewed professional (1, 2); without Penalties; Rest football Portugal (1) crowd matches support?

39 Michael Christian Leitner, Frank Daumann, Florian Follert & Fabio Richlan The Cauldron Has Cooled Down: A Systematic Literature Review on COVID-19, Ghost Games, and Home Advantage in Football from a Behavioral Science Perspective

How does spectator presence affect Analysis of football? disciplinary Home sanctions, Spain (1, 2); 2021 / advantage match England (1, Fouls; Cards; Wunderlich remains in dominance, 2); Italy (1, Shots; Shots on F; Weigelt PLOS ONE / European betting 10 (2010 Regression 6 11 2); Germany Across 36882 1006 target; Goals; M; Rein R; peer-reviewed top-class market and - 2019) analysis (1, 2, 9); Betting odds; Memmert football home Portugal (1); Points D matches advantage in Turkey (1) played matches without without spectators supporters during the COVID-19 pandemic

40