What happened to Drew Stubbs' power?

2011 was a very strange kind of disappointing year for Drew Stubbs.  Strange because it was pretty good for being a bad year.  bWAR says he was worth 2.9 wins and fWAR claims 2.6.  That's a tick better than league-average, and all while making close to the league-minimum salary.  Any saberist worth his or her salt will tell you that's the kind of value-added player you need to make up a championship-level supporting cast.  It was a strange year because while he hit nearly identically to the year before, he hit considerably worse.  Strange, because while he was far from the biggest problem during last year's failed NL Central title defense, he's one of the players most expected to improve next season.  Strange, because I still have no idea what the hell happened to him.

Well, that's not precisely true.  We know what happened to him.  The Light Tower Power was more like Light Beer Power.  The real question, though, is why.  Here's a look at some of his relevant digits over the past few years (via FanGraphs):

It's important to remember that 2009 was his rookie year and he only saw 196 PAs, but the numbers are included to show continuity.  His truncated '09 season and his '10 season were similar in virtually every aspect.  It's his '11 season that stands out as different, but really in only one aspect:  his diminished power.  His BABIP actually got better and his walk rate and his on-base percentage stayed the same.  But somehow the power numbers fell off quite a bit.  His slugging dropped a full 80 points and his ISO 68 points.  Sure, his K rate has increased every year, but that's been offset to a great extent by an increase in walks.  His batting average has suffered because of it, but his OBP has remained steady.  He's still making roughly the same number of outs, but more are coming via the strikeout and fewer via the pop up or ground out.  Also, check this:  Kid's a speed demon, yeah?  He's only grounded into nine double plays in his 1460 career PAs.  But you know what's even more impressive, in the opposite way?  He's only hit 10 triples.  

So the power fell off precipitously.  Is it because pitchers have figured him out?  If you consider that '10 was his first full season in the bigs, perhaps the power outage can be attributed to a sophomore slump caused by pitchers figuring out and exploiting his weaknesses.  That's a pretty oft-used narrative to explain stuff like this, isn't it?  Here's some pitch type data I found kind of interesting:

Stubbs sees significantly more fastballs and sliders than anything else.  About 3/4 of the pitches he sees are either fastballs or sliders.  I didn't include any other pitch types because they didn't seem significant.  He doesn't see many of them and there was no significant change from one year to the next in that data.  But as you can see, the way pitchers pitched him and what he did with these pitches changed pretty significantly from '10 to '11.  He feasted on sliders and had some slight issues with the fastball in 2010, but the script was flipped in 2011.  And even more interesting is that pitchers actually fed him more fastballs and fewer sliders in 2011 compared to 2010.  So perhaps Stubbs actually adjusted to the league's adjustments?  Or perhaps this is all too small a sample size to make anything of.  Either way, it doesn't help answer our original question.

Could it be a batted ball issue?  Here's some more numbers:

There is some intriguing stuff going on here, but it's a bit conflicting.  Notice the drop in FB% and HR/FB.  So not only did he hit fewer fly balls, but fewer of those fly balls that he did manage to hit ended up over the fence.  This goes a good ways to explain how he went from hitting 22 home runs in 583 PAs in 2010 to hitting only 15 homers in 681 PAs last season.  But then again, check out the line drive %.  His LD% went up a full four points over '10, and we all know that line drives turn into hits (and more extra-base hits) far more often than fly balls do.  So theoretically, that should serve to offset the drop in home runs at least a little bit, right?  

Theoretically, yes.  But even Communism works in theory.  Here are even more numbers:

So as you can see, while he traded off some fly balls for line drives, those fly ball home runs in '10 became line drive singles in '11.  I would have expected more of those line drives to turn into doubles and triples, especially considering Stubbs' speed, but they just didn't.  It seems possible that he hit more solid line drives but many of them dropped in front of the outfielders rather than finding the gaps.  I have no way of verifying this (hit f/x is going to kick some ass, isn't it?), but it makes sense to me. That's the kind of bad luck that won't show up in BABIP.  

So what does this mean for Drew Stubbs next year?  I have no clue.