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November 23, 2009

Ahead in the Count

Zack Greinke and FIP

by Matt Swartz

If the internet made crowd noises, the sabermetrics section would have belted out quite a cheer when Zack Greinke, upon winning his 2009 American League Cy Young Award, uttered, "That's how I try to pitch, to keep my FIP as low as possible."

For a few years now, many of us have cheered Brian Bannister, Greinke's fellow Royal, and who also introduced the Cy Young winner to his new favorite statistic. Bannister has shown an ability to understand the statistics that describe the game he plays better than old-fashioned statistics. Bannister has repeatedly discussed his attempts to improve his BABIP, citing his knowledge of BABIP by count as an explanation of his .262 BABIP in 2007, and then reminding reporters that his xFIP was 4.97 in 2008 when he ran into some bad luck, and his ERA was 5.76 in 2008. This is all exciting for us to hear, but the main problem is that Brian Bannister is not really all that good at it. He clearly is better for knowing the intricacies of the game, and he seems like both an intelligent and friendly person. However, sabermetricians (myself included) have had to ignore that Bannister is just a back-of-the-rotation starter. With Zack Greinke, we have a pitcher discussing Defense Independent Pitching Statistics with the press following the announcement of his 2009 Cy Young Award. That's a whole different animal.

However, what has not really been discussed much since he said that is whether what he describes is a good idea. It is smart for general managers to look at FIP or xFIP or QERA, etc., when determining which pitchers are likely to improve or regress in the coming year, but it is quite different to say that an individual making in-game baseball decisions should minimize his FIP.

I am not suggesting that Greinke does this—to the contrary, he reported throwing more fly balls to allow David DeJesus to prevent runs (thanks to his good Zone Rating), thus lowering his ERA but not his xFIP or his QERA, which look at ground-ball and fly-ball rates, rather than home runs like FIP does. He also discussed avoiding walks and seeking strikeouts in his characterization of minimizing FIP, too. However, I thought it would be important to consider the difference between minimizing FIP and minimizing ERA.

Firstly, recall that FIP is equal to (13*HR + 3*(BB+HBP-IBB) - 2*K)/IP, plus a constant that is approximately equal to 3.2. The idea is that this is a good estimator of ERA, and it clearly has shown to be over time. What that means is that, given how pitchers currently attempt to prevent runs, their FIP is a good way to estimate their ERAs. It does not mean that if pitchers intentionally minimized FIP, it would automatically follow the same rule that it approximated ERA well.