A Study of Balls in Play

About a month ago I sat down and examined some of The Hardball Times’s excellent data on batted ball types. The result is the study The Effect of Batted Ball Types on Balls in Play. I’ve gotten a few comments on it that I wanted to incorporate them into the paper, but I have been so busy with other projects that I haven’t had much time to do so. So, I’m just going to post it as is right now, and maybe I can incorporate the comments I get into the next draft.

In the paper, I try to analyze the impact of batted ball types on pitchers’ BABIP and ERA. DIPS/FIP theory says that pitchers have little impact over balls in play; however, there have been a few studies that find some role for pitchers to affect certain batted ball types. In particular, line drives,infield flies, and the ground ball/fly ball ratio seem to be things pitchers can control. Since THT keeps tabs on all of these stats, I decided to quantify the impact of these batted ball types. Here is a brief summary of the results.

Both LD% and the G/F ratio both affect the likelihood that a ball put into play will be hit; furthermore, these factors impact pitcher ERAs. However, the impact of these factors is much smaller than the three main components of DIPS. We know that pitchers can control walks, strikeouts, and home runs from year to year, and that these factors are significant components of ERA. Without including hit ball types, these three factors explained over half of the variance of ERAs of pitchers for the first half of the 2004 season. Adding the hit ball types does very little to further explain the variance of ERAs.

I’d love to hear any thoughts you have on the subject. In closing, I’d like to thank the guys over at The Hardball Times for sharing this fantastic data with the baseball community. You have done a great service to us all. If you don’t read THT everyday, you should.

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