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clayton kershaw
ERA - 2.22
FIP - 3.10
xFIP - 3.06
SIERA - 3.16
K% - 23.0%
BB% - 5.9%
GB - 47.5%
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jake westbrook
ERA - 2.35
FIP - 3.16
xFIP - 3.33
SIERA - 3.43
K% - 15.3%
BB% - 6.4%
GB% - 59.0%
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clay kershaw is a great pitcher. his ERA predicting advanced stats are all coalescing around a 3.10-ish performance. which is obviously very good.
surprisingly, by a lot of metrics, jake westbrook (v. 2012) is, too. his ERA predicting advanced stats are coalescing around something more like a 3.35 ERA, but, y'know, we'll take it. early in the season, his xFIP remained fairly high, up around the 4.00 mark we are more familiar with. i'm still inclined to say that we're in for some regression. he has an extremely low HR/FB rate, relative to his career (7.7% v. 11.7% career). his batted ball luck is normal (.297 v. .300 career). his LOB rate is lucky, but not lance-lynn-in-april-absurd (79.7% v. 69.4% career).
otherwise, he's getting by, striking out batters a touch more than his career numbers (15.3% v. 13.1%) and walking fewer batters (6.4% v. 7.5%). together that makes for a substantial shift in his K/BB rate (2.42 K/BB v. 1.75 career).
and yes, you can start caring about this now. most of these peripherals - K rate, BB rate, GB rate - start to stabilize around when 200 batters are faced. to date, jake westbrook has faced 189. no more will i shout "small sample size" about these 2012 numbers (at least with regard to those particular peripherals and starting pitchers). with each performance, it becomes more likely we are seeing a new and somewhat better jake westbrook.