Carleton: Rethinking randomness among pitchers and their BABIPs

From Russell Carleton at Baseball Prospectus on April 8, 2013:

I think that we’ve really misunderstood pitcher BABIP over the years.

One of the main tenets of what’s become known as DIPS Theory is that there are three “true” outcomes of a plate appearance from a pitcher’s perspective, and that what happens when the ball is in play is mostly luck. It’s one of those assumptions that’s been around so long that it’s baked into a lot of what sabermetricians hold dear. We have component ERAs that assume that a pitcher should have a league-average BABIP. We confidently state that a pitcher will regress to the league mean as if it were a matter of course. We predict doom for pitchers who have a .260 BABIP and salvation delayed for pitchers who have an “unlucky” .350 mark. “Danger Will Robinson! (Insert name of pitcher) has been running on luck and will collapse any moment now!” makes for an easy article. I know, I’ve written plenty of them. In fact, as recently as last week, I predicted that the Orioles would relapse into mediocrity because four of their main relievers from last year had BABIPs in the .260 range and thus, their success was a vast mirage. Because once the ball leaves the bat, it’s all random chance, right?

At this point, there’s a pretty good consensus that the real answer to the question is “Yeah, but… hang on a minute, there’s more to it.” There are a bunch of logical factors that can influence BABIP.

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Originally published: April 8, 2013. Last Updated: April 8, 2013.