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Saturday, April 30, 2011
Did we get a bunch of good relievers this year?
This is the BABIP for starters and relievers, by year:
Year Starter Reliever
2011 0.294 0.283
2010 0.297 0.298
2009 0.301 0.296
2008 0.301 0.297
2007 0.305 0.299
2006 0.303 0.299
2005 0.295 0.295
2004 0.298 0.297
2004-10 0.300 0.297
As you can see, relievers were very stable between .295 and .299 since 2004. And this year, they are at .283.
There have been about 6500 BIP allowed by relievers so far, so one standard deviation is .0057. The difference between .283 and .297 is 2.5 standard deviations.
We’re happy when we get 1.5 SD as a possible indicator that something might have changed. Maybe. When we get 2 SD, we’re feeling pretty good that we are seeing a non-zero difference. At 2.5 SD, we think that something is definitely going on.
Now, in this case, the starters seem to also be affected somewhat. They dropped 6 points from their baseline.
Compared to just 2010 though, the starters dropped 3 points and relievers dropped 15 points.
If I had to guess, I’d say these are the possible culprits:
1. change in bats
2. change in balls (and we only need change within the standards imposed… that is, the range of standards is so wide, that they may as well, almost, not even have a standard)
3. cold nights (though I’m speaking as a North-East guy… easy enough for someone else to pick up the pieces here and compare BABIP for relievers in different parks)
4. shift in talent
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