A remarkable photo of the ball-bat
collsion (from Champaign News-Gazette)

Welcome to my site devoted to research on the physics of baseball. My particular research interests are two-fold: the physics of the baseball-bat collision and the flight of the baseball. I have done quite a bit of independent research in both areas. I am also heavily involved with several areas of practical interest to the game. One is characterizing, measuring, and regulating the performance of non-wood bats, an area for which I have served on committees advising the NCAA and USA Baseball. Another is exploiting new technologies for tracking the baseball, such as PITCHf/x, HITf/x, and TrackMan, for novel uses in baseball analytics. But this site does much more than catalog my own work. It attempts to provide links to much of the high-quality work done over the past decade or so on various aspects of the physics of baseball. If readers know of a site that I have overlooked, please contact me.

Recent Research Highlights

Testing TrackMan: Just How Well Does TrackMan Work?

an article co-authored by Lloyd Smith, Jeff Kensrud, Eric Lang, and myself and published April 2, 2014 in Baseball Prospectus.


Distribution of spin differences between high-speed video and Trackman for spin values in the range 1100-3200 rpm.

The article reports the results of an experiment we did at Minute Maid Park in Houston in January, 2014, in which we used a pitching machine to project fly balls and line drives from home plate. The balls were tracked with the Trackman device in the stadium. Redundant information about the initial velocity vector and spin were determined from high-speed video, and about the landing point from a long measuring tape. The article compares these two sets of data, such as the spin measurements shown in the figure. Conclusion: Trackman works pretty darn well! Read the full article for more details.

The New MLB Tracking System


Jason Hayward runs 80.9 ft along a nearly
straight-line path to make a spectacular diving catch.

At the Sloan Sports Analytics Conference in Boston on March 1, 2014, MLBAM made a presentation about a new tracking system that will effectively track everything on the field: the pitched and batted baseball and all the players. Although not officially announced, it is my understanding from discussions with people in the know that the new system is a merger of radar and video technology, taking full advantages of the strenghts of each. Doppler radar is the natural technology for tracking the baseball. Video is the natural technology for tracking the players on the field. Together, they offer a powerful tool that has the potential to revolutionize baseball analytics. A great example of how the tracking technology might be used in broadcasts is shown in this clip. The new technology is a partnership between Trackman for the Doppler radar and Hego for the video. The new system will be installed at Miller Park in Milwaukee, Target Field in Minnesota, and Citi Field in New York for 2014, with a rollout to 29 USA parks (with Toronto still under discussion) for 2015. It is still not known how much, if any, of the data will be publicly available. As I learn more about this new technology and the MLB plans for rolling it out, I'll be posting at this site.

Trevor Bauer Pitch Design


Link to a slow-motion YouTube video showing the spin on different types of pitches. The video is superbly narrated by Cleveland Indians pitcher Trevor Bauer (@BauerOutage), who discusses pitch movement from a pitcher's (as opposed to a physicist's) perspective. This video is a must-see for all the PITCHf/x and TrackMan data analysts.

D1 Committee Changes to Flat-Seamed Baseballs for 2015 Championship


Press release by the NCAA announcing a change to the baseball used in Division I championship play starting in 2015. See also the earlier story, NCAA Concludes Study on Ball Seams, by Aaron Fitt that was published in Baseball America October 2, 2013. The article reports new measurements done indpendently by the Sports Science Laboratory at Washington State University and by Rawlings. These measurements show that the air drag on the MLB flat-seam baseball is considerably less than that on the NCAA raised-seam baseball. In the WSU studies, baseballs were launched at a speed of 96 mph, a vertical launch angle of 250, and with 1400 rpm of backspin. Under these conditions, the flat-seam and raised seam balls traveled mean distances of 387 and 367 ft, respectively, a 20 ft difference. The switch from BESR to BBCOR bats starting in 2011 reduced fly ball distances by approximately 35 ft and home runs by a factor of two. Scaling roughly from these data, I estimate that the change from flat- to raised-seam baseballs will result in a >50% increase in home run production if used for an entire season, relative to 2011-2013 numbers using BBCOR bats. That is, more than half of the home runs lost with the new bats will be restored.

Modern Techniques for Evaluating Hitting


Batting Average for Balls in Play (BABIP) versus batted ball speed and vertical launch angle.

Link to slides of a talk I gave at the August 2013 Saberseminar at Boston University. The slide above shows that if a ball is hit hard (> 90 mph) and at a launch angle in the range 10-12 degrees, it will result in a hit almost 100% of the time. The data are from the April 2009 release of HITf/x.