Coming up with BERA… like its [almost] namesake might say, it was 90% mental, and the other half was physical. OK, maybe he’d say something more along the lines of “what the hell is this…” but that’s beside the point. By BERA, I mean BABIP-estimating ERA (or something like that… maybe one of you can come up with something fancier). It’s an ERA estimator that’s along the lines of SIERA, only it’s simpler, and—dare I say—better.
You know, I started out not knowing where I was going, so I was worried I might not get there. As you may recall, I’ve been pondering pitcher BABIPs for a little while here (see article 1 and article 2), and whereas my focus thus far had been on explaining big-picture, long-term BABIP stuff in terms of batted ball data, one question that remained was how well this info could be used to predict future BABIPs. After monkeying around with answering that question, though, I saw that SIERA’s BABIP component could be improved upon, so I set to work in coming up with BERA. In doing so, I definitely piggybacked off of FIP and a little of what SIERA had already done. You can observe a lot just by watching, you know. I’m also a believer in “less is more” (except for when it comes to the size of my articles, obviously), so I tried to go for the best compromise of simplicity and accuracy that I could.
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In my last post on explaining pitchers’ BABIPs by way of their batted ball rates, I was very careful to say that it was applicable in the long run, as it’s hard to be accurate over a short number of innings pitched, due to all the “noise” in BABIP (Batting Average on Balls In Play). I only used pitchers with a qualifying number of innings pitched (IP) in the calculations, for that reason. After writing the post, I did some messing around with the data, to find out just how much of an effect IP had on the predictability of BABIP.
Hold on to your propeller beanies, fellow stat geeks: the correlation between xBABIP and BABIP went from 0.805 when the minimum IP was set to 1500, to 0.632 at a 200 IP minimum, down to 0.518 at 50 IP. OK, maybe it’s not that surprising. Still, I thought I’d better show you how confident you can be in my xBABIP formula’s accuracy when you take the pitcher’s innings pitched into account.
The formula, again: xBABIP = 0.4*LD% – 0.6*FB%*IFFB% + 0.235
And remember, that formula is primarily meant to be a backwards-looking estimator of “true,” defense-neutral BABIP. My next article will (probably) discuss another formula I’ve come up with that’s more forward-looking.
Hi everybody, this is my first post here. Today, I’ll be sharing some of my BABIP research with you. There will probably be several more in the near future.
Now, I don’t know about you, but Voros McCracken’s famous thesis stating that pitchers have practically no control over their batting average on balls in play (BABIP) always seemed counterintuitive to me, ever since I heard it about 10 years ago. Basically, my thought this whole time was that if an Average Joe were pitching to an MLB lineup, the hitters would rarely be fooled by the pitches, and would be crushing most of them, making it very tough on the fielders. Think Home Run Derby (only with a lot more walks). Now, the worst MLB pitcher is a lot closer in ability to the best pitcher than he is to an Average Joe, but there still must be a spectrum amongst MLB pitchers relating to their BABIP, I figured. After crunching some numbers, I have to say that intuition hasn’t completely failed me.
This is going to be a long article, so if you want the main point right here, right now, it’s this: in the long run, about 40% or more of the difference in pitchers’ BABIPs can be explained by two factors that are independent of their team’s defense: how often batters hit infield fly balls and line drives off of them. It is more difficult to predict on a yearly basis, where I can only say that those factors can predict over 22% of the difference. Line drive rates are fairly inconsistent, but pop fly rates are among the more predictable pitching stats (about as much as K/BB). I’ll explain the formula at the very end of the article.