The Bizarre Season of Aaron Hill

Tuesday, September 07 2010 @ 06:57 AM EDT

It's no secret that Aaron Hill has been awful this year. However, there's been very little hand-wringing 'round these parts (or anywhere, really) about his struggles. Perhaps it's the homers (he hit #23 in Monday's game), or the excellent defense (though this is a suspect claim according to the numbers). More likely, I think we've all just been assuming he'd come out of the slump at any minute. More than five months later, he hasn't. Why not?

Sometimes, when I dig through stats to find out what's going on with a player or a team or what-have-you, the stats seem to align themselves in layers, and as I delve progressively deeper, each new layer adds new information, usually changing my perception slightly, but sometimes dramatically upsetting what I had previously come to believe. This has never been more apparent than in my examination of Aaron Hill's 2010 season, when the next layer of stats fundamentally changed my opinion on Hill's season no less than three times. Before I take you on this wonderful voyage, though, a little background.

Hill had a great season in 2009. He hit 36 home runs, drove in 108 teammates (some several times!), won a Silver Slugger, and was, along with Adam Lind, one of the offensive leaders of the team - a rare title for a second baseman. He accomplished all this through a combination of improvement in his batted ball profile - his infield fly % dropped about 7% from the previous year - and a dramatic swing in his HR/FB rate. In 2008, an absurdly low 2.4% of Hill's fly balls left the yard - well below the standard 11% for an average hitter. Power hitters, of course, are often able to sustain a higher HR/FB rate, and if Hill really has become that type of hitter, perhaps his 2009 figure of 14.9% is a reasonable expectation. Let's be conservative and say it was a little high, but not by much.

Aaron's BABIP actually hit a career low in 2009 (.288), so I think it's fair to say 2009 looked like a breakout season, and his offensive prowess could be expected to continue, if with a slightly lower home run total.

1. Triple Slash Stats

This is always the first class of stats I look at when assessing a player's season. It gives a quick and dirty view of how often a player gets a hit, how often he walks, and how much muscle he flexes.

There's not much to say here; by these stats, Hill has had a terrible year at the plate, and his line currently sits at .215/.284/.410, even with a recent hot streak.

2. Batting Average on Balls in Play (BABIP)

But wait a second! Upon digging further, it becomes apparent that Aaron has run into some bad luck this year. BABIP is a stat that fluctuates from year to year on a somewhat random basis; once a player establishes a norm (Hill's career BABIP was around .300 coming into this year), their season BABIP tends to fluctuate up to 30 points or so in either direction. There are always some players who see much larger variations, and these are often the players we expect to crash and burn or come back in a huge way, as the case may be.

Aaron Hill is one of those players for 2010. Oh, and that's quite an understatement. Hill has the lowest BABIP in the major leagues. By twenty-three points.

Yeah. Hill's BABIP is an atrocious .204. Carlos Pena is second worst at .227, third is Carlos Quentin at .239. By BABIP, Hill has been by far the unluckiest player in the majors. It's hard to tell exactly what his triple slash stats would look like given an 80 point swing back to his 2009 BABIP (.288), but given the fact that his isolated slugging is almost as good as last year (.195 to .213) and his K/BB ratio is actually better (1.69 to 2.33), it's probably fair to say his season would look something like last year's, when he won the Silver Slugger.

3. Batted Ball Profile

...until you look at the third layer of stats. This is where things get really weird. Check out this (anti) leaderboard, courtesy of Fangraphs, sorted by line drive %:

Name	Team	BABIP	GB/FB	LD%	GB%	FB%	IFFB%	HR/FB	IFH	IFH%	BUH	BUH%
Aaron Hill	Blue Jays	.204	0.65	10.3 %	35.4 %	54.4 %	12.3 %	10.4 %	10	7.2 %	0	0.0 %
Jeff Francoeur	- - -	.259	0.90	13.4 %	40.9 %	45.7 %	13.0 %	7.1 %	12	8.7 %	1	50.0 %
Mark Reynolds	Diamondbacks	.265	0.54	13.7 %	30.4 %	55.9 %	14.6 %	21.2 %	7	8.5 %	0	0.0 %
Rajai Davis	Athletics	.307	1.40	14.5 %	49.9 %	35.7 %	13.3 %	3.9 %	21	11.7 %	2	40.0 %
Drew Stubbs	Reds	.313	1.15	14.5 %	45.7 %	39.8 %	9.6 %	13.0 %	17	12.9 %	3	30.0 %
Carlos Quentin	White Sox	.239	0.76	14.7 %	36.8 %	48.5 %	13.6 %	14.8 %	8	6.5 %	0	0.0 %
Alex Rodriguez	Yankees	.276	1.15	14.7 %	45.7 %	39.6 %	9.8 %	14.7 %	12	7.3 %	0	0.0 %
Jose Bautista	Blue Jays	.249	0.59	14.9 %	31.6 %	53.5 %	14.4 %	21.4 %	11	9.2 %	0	0.0 %
Carlos Pena	Rays	.227	1.15	14.9 %	45.6 %	39.5 %	10.8 %	23.4 %	10	7.8 %	4	80.0 %
Troy Glaus	Braves	.276	0.91	15.2 %	40.5 %	44.3 %	5.1 %	11.7 %	4	3.2 %	0	0.0 %
Brennan Boesch	Tigers	.307	1.10	15.3 %	44.4 %	40.3 %	17.1 %	10.9 %	9	6.3 %	0	0.0 %

Yes, you read that right. This is the second important stat in which Hill is an extreme outlier. He has the lowest line drive % in baseball. By over three percent. Line drives are the best kind of batted ball since they fall for hits much more often than ground balls, fly balls, or anything else. Over his career, Hill has generally hit line drives around 20% of the time; this year, he's down to 10%. That's a huge change.

Of course, those balls have to go somewhere, and in this case Hill's fly ball percentage has increased by a whopping 13.4% (he shaved a few points off his ground ball % from 2009 as well). It's as if he consciously changed his swing based on all those home runs he was hitting. If he could hit 36 as a line drive hitter, imagine how many he'd smack with an uppercut?

So now we've swung back to the perception that Hill is indeed having a very bad year, as indicated by the number of line drives he hasn't been hitting. This seems to be a reasonable explanation for his bizarrely low BABIP.

4. xBABIP

Now the good news. I just found this handy little xBABIP Calculator at the Hardball Times, which attempts to predict a player's BABIP based on their batted ball profile. Turns out that based on his LD%, GB%, etc., Hill's BABIP should have been around .285, or just about the same as last year.

Okay, now that's a head-scratcher. His line drive % cut itself in half, and we can expect his batted balls to turn into hits at the same rate? The answer is that, according to this tool, Hill under-performed his BABIP last year as well, by about 25 points. Now that's an interesting result in itself; Hill was great last year. He hit 36 home runs! And he was unlucky?!

But actually, this result, the 2010 result I mean, doesn't seem too outlandish when one examines the above table. All those guys have low line drive rates (though not as low as Hill, admittedly) and their BABIPs seem to center around .270 or .280.

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So another layer of stats has once again turned the analysis on its head and we're back to the "Hill is fine" conclusion. At least that's what the numbers say - I still find it hard to resolve a 10% line drive rate with an above-average hitter. It seems that Hill is able to turn this trick on the strength of his above average power (.200 ISO) and strong plate discipline (his strikeout rate, never very high to begin with, has actually gone slightly down in the last two years as he's added power).

Regardless, I hope to see him go back to 2009 form. Hill always seemed like a good line drive hitter; I'd rather he hit 20 homers a year with a high batting average and lots of doubles. Somehow that just seems safer. I don't know. But anyway, the lesson for today is, even if he stays the same hitter he's been in 2010, he should still be a productive hitter.

Now, defense is another issue. Despite his sterling reputation, UZR says Hill has only had one great season defensively (2006), and otherwise he's been about average. Some have mentioned a future move to third base, and Hill has even commented that he'd be open to such a move. At this point though, nobody's knocking the door down at either position, so I say you keep him in the middle infield. Perhaps when Hechavarria is ready one of him or Escobar moves to second and Hill shifts to third. But that's a post for next year (or sooner, hopefully!).

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