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Deceptive First/Second Half Splits

A few weeks ago a reader asked me if I was concerned about Dan Haren's second half decline.  After all, Haren posted a 2.01 ERA in the first half and a 4.62 mark in the second.

I set out to check Haren's splits, and quickly found that he was strong for the season's first four months but had ERAs near 5.00 in the final two.  So now our concern is over a 12-start span.

Then I checked Haren's splits at FanGraphs.  FanGraphs gives you a pitcher's peripherals, BABIPs, and xFIPs by month.  This is an excellent development for fantasy leaguers.  Haren's August featured a 4.86 K/BB.  Typically excellent control, slight dip in strikeout rate but not a source of concern.  His problem was allowing eight home runs in those six starts.  I'd consider that a fluke.  XFIP normalizes a pitcher's home run per flyball percentage, and that showed a 3.64 ERA for August compared to his actual 4.95 mark.

In September/October, Haren was bitten by BABIP instead of HR/flyball.  His peripherals were sharp, but his BABIP was .352, leading to a 4.79 ERA.  His xFIP was 2.96.

So all this second half Haren concern really just boiled down to four extra homers in August and more hits dropping in in September/October.  With samples that small, I can't muster concern for Haren's 2010 second half.  Maybe he really will struggle in the second half for some reason, but his 2009 numbers didn't predict it.  I encourage you to go month by month, especially for pitchers, and see if there really was a problem.

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