Thinking About Fastballs

With Andy Pettitte set to start tonight against the Blue Jays, I thought it'd be interesting to look at what might have produced his lowest Batting Average on Balls In Play since 2005 with the Astros.  He sits at .312 this year, compared to an average around .330 for the last 3 years.  Why hasn't this translated into a great statistical year for him?

The obvious culprit is LD%.  There's a direct correlation between LD% and BABIP; usually we expect BABIP= LD% + .120 (though, for you real stat geeks, here's something to think about).

Pettitte's LD% is at 18.2%, his lowest rate within FanGraph's data (2002-present).  That explains the drop in BABIP (expected .302 vs .312 actual).

But why?

Andy's healthy this season, for one.  His fastball is averaging .2MPH faster than last year, his cutter .1MPH faster, his curve 1.8 MPH faster, his changeup 1.5 MPH faster.  The difference in speed should slightly change the look and break of his offspeed stuff, though I hadn't noticed that Pettitte's curve had visibly changed.  On the other hand, the change would have to be equivalent to Phil Hughes' big 12-6 curve vs his new tighter one for me to really notice.

I think the bit reason is pitch selection.

Last year, Andy fell a little in love with his cutter.  He threw it 27.9% of the time, the highest rate in FanGraph's records.  This season, his cutter is back to a more typical 19.7%, still second highest of the recorded rates, but withing a couple percentage points of average.

His changeup, which nearly disappeared from his repetoire last season, is back once every ten pitches.  Andy is also throwing his 4-seamer more than he has since coming back to the Yanks.  I'd expect all of this to equal good things for the Texan.

But the really telling stat is his First Pitch Strike Rate, which is only 59.6% compared to 61.8 last year.  That's his lowest rate since 2004 with the Astros.  He's falling behind hitters and then giving up free passes at his highest rate since, again, 2004.  This is no coincidence.  It also explains the rise in the number of 4-seamers he's thrown; he's behind in the count and he needs a strike.

Watch Andy closely tonight.  He's got to start off every at-bat right; he's probably got the best defense behind him since the mid-90's.  Let them put it in play, just stop putting them on for free.