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Matt Cain Regressing to the Mean?

August 16, 2012

Generally, pitchers who give up a lot of flyballs will give up a significant amount of homeruns, but Matt Cain has been the exception to that rule. Matt Cain has always been a mystery to sabermetricians and baseball analysts because flyball pitchers traditionally cannot sustain low HR/Flyball ratios. Cain has a 6.9% HR/FB (I am discounting 2005 where he started only 7 games), which is very low compared to the league average from 2006 to 2012 of 9.97% or essentially 10%. Cain, with that continuously low HR/FB rate allows his ERA to continuously outperform his xFIP, which takes into account the general unsustainability of low HR/FB rates. Cain’s career ERA of 3.32 significantly out performs his career xFIP of 4.17.

Last year, Cain had a career year when it came to the HR ball. He had a 3.7% HR/FB rate and only gave up 9 HRs in 221.2 innings, which is outstanding and in many ways unsustainable. This year is a bit different though — Cain as of today has given up 18 HRs and has a 9.8% HR/FB rate in contrast to the league avg of 10%; Cain is essentially league average in a department he has excelled in throughout his career.

Him regressing to the mean is one of the possible explanations for his spike in HR rate. Another answer might be linked to his significant improvment in strikeout rate and walk rate. This year Cain is hitting career highs in strikeout rate (8.34 K/9 vs his career 7.62 K/9) and reaching lows in walk rate at 1.89 BB/9 vs 3.09 BB/9. Cain is throwing more strikes then ever before. This is indicated by the higher Zone% of his pitches vs the career averages shown in the Fangraphs chart below.

Has the greater amount of strikes be lead to more hittable balls over the plate more often? This was my initial feeling but Cain’s BABIP has not seen a spike — his .265 BABIP exactly matches his career rate of .265.

Cain in 2012, according to Brooks Baseball, has been having problems with his cutter, which has a HR rate of 1.11% and his 2-Seamer which has a a 2.5% HR rate both high compared to his 4-Seamer (.66 HR%), Change (.89%), and Curve (.79%). Brooks Baseball says Cain gave up 0 home runs on his 2-Seamer in 2011 and that he has only started throwing the cutter in significant amounts this year, so it could be the addition of the cutter which has been giving him problems.

This goes back to the titular question; is Cain’s pedestrian HR/FB rate a result of him regressing to the mean, or is it a function of him throwing more strikes, or even just one new pitch such as the cutter that has been giving him problems? I would probably believe its a combination of all of these and a confluence of factors rather than one significant change. We really will not know if this season is just a minor blip of small sample size or a new trend in Cain’s career until we can observe a few more seasons with his enhanced walk, strikeout rate, and cutter.  Still, even with the spike in home runs, Cain has been awesome this year to the tune of a 77 ERA- and I don’t think the long ball has been a significant enough problem for fans to worry about.

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