The Zambrano/Bonderman Conundrum

A conundrum is loosely defined as anything that puzzles… so it makes perfect sense to use the term when describing the anomaly present in the ERA and FIPs of both Carlos Zambrano and Jeremy Bonderman. We’ve written about pitchers either outperforming their FIP or failing to live up to it plenty of times here, but, in probing the last three calendar years feature recently instituted on the leaders page, it appears that things tend to even out a bit. Except, of course, with regards to Zambrano and Bonderman.

Sixty starting pitchers qualified for inclusion over the last three calendar years and they produced the following averages:

ERA-FIP: 0.12
BABIP: .303
LOB: 71.8%
K/BB: 2.48
HR/9: 0.98

One standard deviation of the ERA-FIP is 0.28, meaning we can expect about 2/3 of the data to fall within the -0.16 to 0.40 range; additionally, 95% of the data can be expected to fall within the -0.44 to 0.68 range. Of the group of sixty pitchers, just two fell beyond the 95% confidence interval: Carlos Zambrano at -0.53 and Jeremy Bonderman at 0.83.

Now, one potential reason that someone like Zambrano consistently posts better ERAs than his FIP would suggest could deal with his BABIP: the average BABIP of this group in this span is .303 and Zambrano comes in at .273, a full thirty points lower. On the other end of the spectrum, Bonderman comes in at .325, over twenty points higher. In fact, when looking at the eighteen pitchers who fell beyond one standard deviation of the ERA-FIP mean, the nine higher than 0.40 ranged from .297-.332 in BABIP while those below -0.16 ranged between .269-.309.

I actually discovered whilst writing this post that a question regarding Zambrano outperforming his FIP was posed in the Inside the Book mailbag, to which MGL mentioned the possibility of him posting a lower than average BABIP after concluding that it is definitely possible for certain pitchers to post certain types of BABIPs. This is definitely the case. As MGL also noted in the mailbag, “FIP is a very good at eliminating the noise in BABIP, which allows us to get a better estimate of a pitcher’s run prevention skill, in the short run. In the long run, ERA, RA or ERC is MUCH better because it captures the differences in BABIP skill among pitchers, as well as the other things I mentioned above that contribute to a pitcher’s run prevention skill but are not addressed at all in FIP (like WP rate).”

So, one reason these two guys are constantly posting ERAs much better or worse than their FIP would suggest could be that they have posted above or below average BABIPs with enough regularity to show they have some type of control over it; in that regard, their ERA would be a better indicator of run prevention. Then again, they might not have control over their BABIP and this could all even out, but it would seem that this is a very likely cause at this juncture.





Eric is an accountant and statistical analyst from Philadelphia. He also covers the Phillies at Phillies Nation and can be found here on Twitter.

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Detroit Michael
15 years ago

If a significant percentage of starting pitchers had the ability to consistently produce BABIPs significantly different from .303, then wouldn’t we expect to see more than 2 out of 60 starters with FIP- ERA past the 95% confidence level? While we ought to be open to the possibility that Zambrano and/or Bonderman are exceptions, the data you presented suggests (to me anyway) that variations from BABIP really are random.

I am aware of the Tom Tippett research from a few years ago suggesting that pitchers do have some weak control over their career BABIPs (at least historically — the study didn’t focus on the current decade), so my guess is that pitchers’ BABIP isn’t literally random. I’m just saying that your post isn’t very persuasive on the matter.

Are there reasons why Zambrano and Bonderman are unique? Can we look at other pitchers who share their unique characteristics and see if their BABIPs on average differ from .303?