What the Heck Is Pitchf/X? by Mike Fast
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The Hardball Times Baseball Annual 2010 What the Heck is PITCHf/x? by Mike Fast here is a revolution underway in baseball. It is a assumes that the baseball experiences constant accel- Tquiet revolution, not as controversial perhaps as eration; i.e., that the forces on the ball do not change 00-pitch limits for starting pitchers, but in the end, the in any meaningful way during its flight. This is a good changes it brings may be more influential. assumption for rapidly spinning baseball pitches, and The revolution debuted on Oct. 4, 2006, in an Amer- almost all pitches fit this criterion. The notable excep- ican League Division Series game between the Oakland tion is the knuckleball, which spins very slowly, causing Athletics and Minnesota Twins at the Metrodome. the drag force on the baseball to change depending on Most of us had no idea that, as Esteban Loaiza threw the seam orientation. However, it turns out that the a first pitch strike to Twins leadoff batter Jason Kend- PITCHf/x constant-acceleration model works fairly all, Sportvision’s PITCHf/x cameras were tracking the well for knuckleballs, too, with only slightly larger trajectory of the pitch, identifying its speed, break and errors than for other pitch types. location in real time and transmitting this information What information does Sportvision and MLBAM for use by broadcasters and Major League Baseball’s collect about the game? We already mentioned that Gameday web application. the PITCHf/x tracking software calculates the posi- Sportvision is a TV sports broadcast effects company tion, velocity and acceleration of the pitched baseball based in Mountain View, Calif. Its engineers are most in three dimensions. It also puts a date-time stamp on famous for creating the glowing FoxTrax hockey puck each pitch. The PITCHf/x operator is a Sportvision and the yellow first-down line superimposed on football employee on site at each baseball game. The operator is broadcast video. Its current bread and butter product is responsible for monitoring the calibration of the system GPS tracking of race cars during NASCAR races, and during the game and for recording the top and bottom it provides this information to broadcasters and online of the strike zone for every batter from the center field to race fan subscribers. So when Sportvision turned camera video. its attention to baseball, it brought a strong pedigree in Other information is entered in real time by a string- applying technology to sports broadcasts to bring fans er, an MLBAM employee also at the game, into software new insight into their sports. for transmission to Gameday. That person records the To track the flight of each major league pitch precise- result of each pitch (for example, ball, called strike, ly, Sportvision has installed a pair of cameras in each swinging strike, foul ball or in play). The stringer notes stadium, in the stands above home plate and first base. any pinch hitters or defensive substitutions and records Twenty-eight of these installations occurred during the result of each at-bat (for example, single or fly out), the 2007 season, and the other two, in Baltimore and the movement of baserunners, and the location on the Washington, were completed before to the 2008 season. playing field where the batted ball is fielded. MLBAM Detailed tracking data were recorded for about a third software attempts to classify the type of pitch that was of the pitches thrown in the major leagues in 2007 and thrown (for example, fastball or slider). more than 95 percent of the pitches in 2008 and 2009. All of this data is available free on the MLBAM Sportvision made these data available in real-time to GameDay website. As a result, between the PITCHf/ Major League Baseball Advanced Media (MLBAM) for x data on the trajectory of the pitch and the MLBAM use in its online Gameday application and to broadcast- stringer’s record of game events, we have a wealth of ers such as ESPN for its K-Zone strike zone graphic. information on every baseball game. How Do We Get The Data? Differences Between Coarse And Fine Data Sportvision’s tracking software takes the approxi- With this abundance of fine-grained data, particu- mately 20 images of the baseball acquired during its larly the detailed record of the speed and movement of flight from the pitcher’s hand to home plate, determines every pitch, a new analytical approach must be crafted the 3-D ball location on the baseball field from each and new common language developed for discussion image, and finds the pitch trajectory that best fits these among fans and analysts. Our current language of 20 or so points along the path of the pitch. The software baseball has its roots in the 9th century with Henry What the Heck is PITCHf/x? Chadwick, inventor of the box score. Games have been game to another? What does “movement on a pitcher’s described in terms of hits and outs, bases and runs. fastball” even mean? This context, too, must be devel- These are very clear but coarse measuring sticks, but oped over time. they are the ones we have come to understand. We can converse in that language without needing to explain the Spin Deflection context. Debates about the merits of various analytical I’m not a fan of the term “movement” to describe a approaches do not require arguments about founda- pitch. How a ball moves depends on its initial velocity tional principles. Instead, the validity of the base-out and the forces on the ball in flight, which include grav- counting system and much of the long analytical history ity, drag, and the Magnus, or spin, force. It has become built atop it is assumed. popular for analysts to use the term “movement” to Within the last decade, the availability of detailed refer to the deflection of the ball due to the spin force. fielding data has begun to shift this paradigm, if only I prefer to refer to it as spin deflection. perhaps at the margin. It is widely recognized that Speed and the spin characteristics of a pitch are our fielding is not well measured by simply recording which primary ways to identify what type of pitch a pitcher fielder recorded each out. More detailed data on the path threw. A pitcher’s grip and wrist motion on release of the batted ball are desirable for determining which apply spin to the baseball, and this spin produces force fielder should be assigned credit or blame for fielding on the baseball that causes it to veer. The topspin on or not fielding a ball and how much credit or blame he a curveball causes it to veer downward more than it should get based on the difficulty of the play. However, would from gravity alone. The backspin on a fastball since most of this data is proprietary, the impact on the causes it to drop less than it would due to gravity. Most language of the game has so far been small. pitches also have some sidespin, which causes the ball With the wide availability of PITCHf/x data, howev- to veer to the left or right. er, a seismic shift in the language of baseball and its analysis is beginning. The description of a pitch is now The Physics Of Baseball on a continuum between fast and slow, breaking left One of the more fascinating results of the PITCHf/ or right, up or down. How do we make sense of these x data set is the extent to which it has expanded our detailed data? Where is the context? knowledge of the physics of baseball. Dr. Robert Adair Radar gun readings have established some context is well known for his excellent book, The Physics of Base- for the speed of a pitch; as a result, that information ball, which he wrote in 987 as the result of research from PITCHf/x has been the most quickly adopted he undertook at the behest of then National League and easily understood, although no one really knows president Bart Giamatti. In fact, Adair served as an yet what a difference mph of speed on his fastball adviser to Sportvision in the early days of PITCHf/x means to a pitcher’s effectiveness. These fundamen- development. tal concepts will have to be investigated, understood However, our understanding of the physics of pitched and communicated over time. Almost every baseball and batted baseballs has improved immensely simply fan has an intuitive understanding of the difference through the availability of such a large, high-quality between a .260 hitter, a .290 hitter and a .320 hitter. data set. We have learned a great deal about the drag One is average, one is good, and one is among the best and spin forces on a baseball. Dr. Alan Nathan has in the game. I suspect some day we will have a similar lead the investigation into many topics of interest, along intuitive understanding about pitch speeds. However, with a crowd of others, and you can read more at his that context is only now emerging. We have so much Physics of Baseball website (see References section). new information that it is difficult to assimilate it quick- ly. We should remember that our current analytical Gameday Application framework of understanding was developed over more Many people’s first exposure to PITCHf/x is through than a century. MLBAM’s Gameday application. (For those who are The new detail we have about pitch movement unfamiliar with Gameday, it lets fans follow the game is particularly challenging in that we have almost no online.