Tuesday, December 12, 2023
FIP and xwFIP
Another excellent article from Josh, incorporating BABIP through the lens of xwOBAbip to give us xwFIP. In other words, he keeps the actual BB, SO, HBP, HR while replacing the rest of the BIP by using the xwOBA data. And it gives us a step forward.
FIP of course remains ubiquitous and offers the ideal Naive method for pitcher evaluation. The amount of effort to calculate FIP is almost non-existent, while also being completely transparent. And as we know, FIP represents a pitcher's past performance better than ERA does. Using FIP unaltered for future prediction is a happy byproduct of its construction, but not its raison d'etre. FIP was, is, and always will be an evaluation of a pitcher's past performance.
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Pitchers
I left this comment in his blog… but a wrinkle on this would be to convert his hxwOBA to hxERA. Which I *think* you’ve done as
hxERA = ERA.lg*(hxwOBA/hxwOBA.lg)^2
* hxwOBA = “half-expected wOBA” = weightings of 0.7 and 2.0 for BB/HBP and HR respectively, but LA/exit velo-based wOBA coefficients for BIP.
* hxERA = “half-expected ERA”