I have looked at ground balls and fly balls in isolation and how increasing ground ball rates interact with a pitcher’s home run and slugging percentages. What about plate appearances that do not end with a batted ball? I took a look at strikeouts and walks as well and found them both to decrease in absolute frequency as ground ball rates rose.
That is not unexpected since the more ground balls a pitcher gets, or more fly balls, or anything really, the fewer plate appearances there are available to be ended in a strikeout or a walk. Still, it was worth a look at these absolute frequencies since the raw strikeout and walk totals are the inputs into FIP-based metrics.
I was not satisfied with looking only at those absolute rates however. I wanted a fairer judge of whether gunning for ground balls had a meaningful effect on a pitcher’s ability to get strikeouts or prevent walks. My answer to that was to change the denominator from plate appearances to plate appearances that did not end in a batted ball.
Imagine two pitchers, one a Brandon Webb-esque groundballer, the other a Jered Weaver-type flyballer. Each of these two pitchers have a certain amount of batters faced that end in a strikeout, a walk, a hit batsmen or some other freak occurrence that was not a batted ball. Of those plate appearances, what percentage ended in a strikeout? What percentage ended in a walk?
It turns out to not have a meaningful difference. Fly ball pitchers might get more strikeouts and fewer walks as a percentage, and it might even be statistically significant, but the rate of change here is so small though as to be immaterial. The expected difference between the two biggest reasonable extremes in ground ball rate (30% to 60%) amounts to fewer than five strikeouts or walks over 200 innings pitched.
Given that there appears to be little change in strikeout and walk rates and an obvious decline in home runs as ground ball rates increase, how does a pitcher’s ground ball rate affect overall performance? That’s next.
Matthew Carruth is a software engineer who has been fascinated with baseball statistics since age five. When not dissecting baseball, he is watching hockey or playing soccer.