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

The Physics of Fielding

This article appeared in the February 18, 2015 edition of The Hardball Times and was written by physics professor Dave Kagan. Dave uses StatCast data to do a quantitative analysis of the physics of fielding, utilizing a Lorenzo Cain catch as an example. This article reminds me of an earlier article by ex-MLB pitcher Dave Baldwin and engineering professor Terry Bahill entitled A Model of the Bat’s Vertical Sweetness Gradient. The article looks at how the ball-bat offset affects the batted-ball trajectory, especially the hang time, and from that makes quantitative statements about the probability that the ball will be fielded.

Inertial Sensors for Baseball

The Zepp (left) and Blast (right) knob-mountable bat sensors.

This page contains links to articles about the use of inertial sensors that are attached either to the knob of a bat or to a person. They are used to track motion and orientation. For example, they can be used to map out the trajectory and orientation of a bat during the batter's swing. They can also be used to map out the motion of a pitcher's elbow during the windup and delivery. The links are not meant to be a complete list but sufficient to give the reader a flavor of how these devices work and what they can be used for. Although I have not yet contributed to the development or testing of these devices, I expect that will change with the new year.

How Far Did That Fly Ball Travel? (Redux)

Alan M. Nathan, Lloyd Smith, Jeff Kensrud, Eric Lang, Baseball Prospectus, December 9, 2014

This article is a followup to a previous article How Far Did That Fly Ball Travel? published in Baseball Prospectus on January 8, 2013. It is an account of our experiment at Minute Maid Park in Houston, January 2014. The object was to measure the distance of fly balls projected into the outfield with a fixed initial speed of 96 mph and vertical launch angle of 280. In an ideal world, all baseballs would land at the same place. But as the figure shows, there is great variation in the distance, depending not only on the type of baseball (NCAA, MiLB, MLB) but even which baseball of a given type. Interestingly, the data also show very little variation in distance for backspin rates in the range 2200-3200 rpm. An important conclusion is that variation in fly ball distance is due much more to ball-to-ball variation in the drag (for example, due to small differences in surface roughness) than to variation in spin. Further evidence for ball-to-ball variation of drag comes from PITCHf/x data, about which an article will be written soon. Further evidence for MLB home run distances being nearly independent of spin will also be presented in a future article.

NOTE: If you are not able to access the Baseball Prospectus article, you read it here.

The Physics of Baseball, 1920's style

My analysis of an article from 1920 about the physics of a Babe Ruth home run, appearing in the middle of the season when Ruth hit 54 home runs, nearly doubling his own single-season record of 29 from the previous year. We know a lot more about the physics of baseball now than we did nearly 100 years ago. As a result, there is some wrong physics in the article. I discuss all of that in my analysis. My thanks to Greg Rybarczyk (@hittracker) for calling this article to my attention.

Bats: They're Not Just Flying Mammals. The Science of the Baseball-Bat Collision.

Slides of my talk at the 4th annual Saberseminar, Boston University, August, 2014.


Marco Scutaro "squares up" and hits a line drive single in 2012 NLCS.

In the presentation, I talked about general features of the baseball-bat collision, including how the batted ball speed depends on pitch and swing speed. Also discussed are the role that vibrations play in determining the "sweet spot" of the bat; the factors that contribute to bat performance; the reason why aluminum generally outperforms wood; and the use of science to regulate the performance of bats, especially as applied to the so-called BBCOR bats used by the NCAA and high schools.