Wednesday, June 01, 2011

Phil Humber's BABIP, K9, BB9

This analysis is a great example of the problems that can occur with using statistics without fully understanding their meaning:

"So what are we to make of Humber, where did this come from, and more importantly, can it last?

The short answer to that last question is, no. No, he cannot maintain a 2.85 ERA, few pitchers can, and those who sport .210 BABIP marks definitely cannot. But there are other things about his performance in 2011 that he can carry forward. Primarily, an improved BB rate that, at 1.95/9IP is more than a full walk less than his career average of 2.99. If he can pump his K rate back into the mid-five range, with his typically solid (if unspectacular) ground ball rates, that could translate into the sort of sustainable performance you'd expect of a #4 or #5 starter."

For instance how did Humber get an "improved BB rate". You would think the answer would be by walking fewer batters. While he is walking slightly fewer batters, that isn't what is driving his BB9 down significantly.. Instead he has improved his walk rate by getting more batters out and thereby increasing his IP. Its the same reason his K9 is down, And those increased outs can all be traced to that dramatic improvement in his BABIP. In other words, all three statistics reflect the same change in performance. Its possible that Humber will sustain an above average BABIP, most successful pitchers do, but no pitcher has ever sustained one around .210. And, as his BABIP increases, the number of outs will go down and his BB/9 and K/9 will both go up.  If goes up to the league average of .300, he is likely in trouble.

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