SABR

Nathan: Just how well does TrackMan work?

From SABR member Alan Nathan, along with Jeff Kensrud, Lloyd Smith and Eric Lang, at Baseball Prospectus on April 2, 2014:

Let us begin by answering the question posed in the subtitle: Pretty darn well! Now let’s see how we arrive at that conclusion.

Back in early 2013, one of us wrote a Baseball Prospectus article entitled "How Far Did That Fly Ball Travel?". The article posed the question: How well does the initial velocity vector (speed and angles) determine the landing point of a fly ball? Utilizing home run data from actual MLB games, it was determined that the initial velocity vector poorly determines the landing location. Much of the rest of the article was devoted to speculation about why that is the case. Three possible reasons were identified and investigated: variation in wind, backspin, and the baseball itself. The latter is the most intriguing possibility, since variation in the seam height and/or surface roughness of the ball might have a significant effect on the air resistance experienced by the ball.

As a follow-up to this research, we decided to do an experiment under more controlled conditions rather than use MLB game data. Since we wanted to eliminate wind as a possible factor, we approached the Houston Astros organization about using Minute Maid Park (MMP) with the roof closed for our experiment. To our delight, they agreed, so the four of us gathered in Houston for two cold days this past January to perform the experiment.

A very fancy pitching machine, designed and constructed by the Washington State part of our collaboration, was set up at home plate and was used to project baseballs either as fly balls or as line drives, with complete control over the initial speed, angles, spin rate, and spin axis, as well as the baseballs that were used. A high-speed video camera viewed the initial part of the trajectory in order to measure both the initial velocity vector and the spin rate. The landing point was measured with excellent precision using a tried-and-true, albeit old-fashioned technique: a very long measuring tape. But the really neat part of the experiment was that we had redundant measurements of all of those quantities (landing point, spin rate, initial speed and launch angle) using the Trackman unit that is permanently mounted in MMP.

Read the full article here: http://www.baseballprospectus.com/article.php?articleid=23202

This page was last updated April 3, 2014 at 6:12 pm MST.

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