This article is part of our The Z Files series.
Lesson learned: less sausage, more meat. Understanding how the sausage is made is certainly a worthwhile endeavor but there's only about eight weeks before drafts pick up in earnest, so there will be less bandwidth on theory and more on application.
This week's discussion will continue the notion of breaking average exit velocity (AEV) into components, with flyballs the focus. By means of reminder, here is the 2019 league average velocity component data:
Pitches travel with a downward trajectory. In order to transfer the most energy to a batted ball, the swing path should match the trajectory, hence an uppercut. This explains the difference between grounders and flies. Neither are centered, but the upward trajectory of the swing transfers more energy to anything lofted.
The bulk of today's discussion will revolve around a concept Mike Podhorzer from Fangraphs introduced several years ago. Home run rate correlates very well with average fly ball distance (FBD). So much so, in fact, an expected home run total can be determined for every hitter and compared to their actual performance. Just like comparing any stat estimator, outliers can be identified and evaluated.
Parsing out flyball homers and comparing HR/FB (home run per fly) to average FBD, the correlation coefficient is .77. Intuitively, flyball distance should correlate with AEV on flies. Launch angle matters, but there should be some relationship. Sure enough, the correlation coefficient is a strong .90. Flyball AEV correlates to