Mains: What Deserved Run Average tells us about groundball pitchers

From SABR member Rob Mains at Baseball Prospectus on August 11, 2016:

Back in June, I took on the issue of groundball pitchers. Well, more specifically, I took on the issue of groundball pitchers and Bill James’ antipathy toward them. This article was prompted by James’ comment, “If you like Groundball pitchers, you’re welcome to them. I don’t want nothin’ to do with them.” In the article, I looked at pitchers last year. I found that if you rank every pitcher in 2015 by groundball percentage and divided them into deciles, generating more groundballs was correlated fairly strongly to fewer home runs and lower ERA and FIP.


As groundball percentage rises, walks rise a little, strikeouts decline a bit, but more dramatically, home runs decline, because it’s hard to hit a home run on a groundball. That drives a sharply lower ERA and FIP.

I followed up by looking at pitchers from other seasons. I had already done the numbers for 2015, so I went back a decade at a time, to 2005, 1995, 1985, 1975, 1965, and 1955. I found that while the equation more groundballs = better run prevention holds in general, it doesn’t work well in some years, and the relationship is stronger today than it was decades ago. I also found some merit in James’ position, in that both the groundball metric he used (groundball double plays divided by GIDP opportunities) and the pool of pitchers he considered (only those with very long careers) supported his conclusion. However, I stuck by the assertion that in contemporary baseball, if you’re looking at a given pitcher, getting more groundballs is a good thing. It’s not the only thing—among ERA qualifiers, Max Scherzer has the seventh-lowest groundball rate and Justin Verlander the ninth-lowest, and they rank third and sixth, respectively, in PWARP—but it’s a good starting point in pitcher evaluation, all things being equal.

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Originally published: August 11, 2016. Last Updated: August 11, 2016.