Last week I posted the year to year correlations for xStats and their standard variants, and it came up with a few interesting results. The xStats variants were much more consistent year to year, for better or worse, and in general they were better at predicting future performance. Not by much in some cases, but hey, every bit helps, right? It made me curious how it may translate to groups of players with smaller sample sizes, so this week I’ve taken these stats to relief pitchers, with those year on year correlations in mind. Yes, it is frustrating that we only have two seasons to look at, but this is the best we have at the moment so let’s see where it gets us.
As you might remember, vertical launch angle was very consistent (.75) between 2015 and 2016 for all pitchers, and as it turns out this holds true for every innings limit you can imagine. Whether you want to talk about guys with 30 innings, 200 innings, or anything in between. Vertical angle appears to stabilize fairly quickly. So, that begs the question, how does vertical launch angle change batter performance? Hopefully this chart will answer your questions.

Between roughly 10 degrees and about 35 degrees batted balls have high value, with batting average peaking around 13 degrees, slugging around 25 degrees, and home runs around 27 degrees. So, if we know vertical launch angle is stable between seasons, and batted balls between 10 and 35 degrees are bad (for the pitcher), then perhaps aiming for pitchers who have average launch angles outside of that zone would be ideal. Read the rest of this entry »