Monday, November 14, 2011

Aaron Hill And Predictability

After a player has put in seven years of service encompassing 908 games, you have a pretty good gauge on what kind of player he is. Things like luck can cause minor spikes and contrasts, but normally a baseline can be reached. You can forget all about that with Aaron Hill. His career reads like a stock market chart. He started his career as a low strikeout, low power kind of guy. Then suddenly he's hitting 62 homers in two years. Then he goes back to no power again. What the heck? Take a look at just two statistics, his ISO and his wOBA over the course of his career. The following charts give you a visual representation.

How are you supposed to get a feel for what kind of player Hill is by looking at that mess? And those aren't the only statistics that drive you crazy with Aaron Hill. Take his line drive percentage. Here is a list of his line drive percentages during his career: 23.1, 19.2, 20.8, 17.3, 19.6, 10.6 and 21.2. See any pattern there? No, not here either. 

There are a couple of trends you can see though. When he first came up, he hit more ground balls than fly balls. His first three years, his ratio of ground balls to fly balls were 1.5, 1.33 and 1.04. Since 2008, that trend disappeared and he's become a batter who hits more balls in the air. That same ratio since 2008 looks like this: 0.74, 0.96, 0.65 and 0.87. At the same time, after three years of single digits in infield fly pops his rate exploded starting in 2008 and has been in double digits every year since. Perhaps he figured out that chicks dig the long ball. Well, the long ball is fine as long as all the other numbers look pretty along with the homers.

But that's not the case after his breakout year in 2009. He did still hit 26 homers in 2010, but everything else tanked. You would think that the longer Hill plays in the majors that his plate discipline would get better and better. But it's just the opposite with Hill. When he first came up, his O-swing rates (swings at pitches outside the strike zone) were excellent at 15.4 and 18.7 percent his first two season. In his last two seasons, that has ballooned to 31.3 and 29.5 percent--easily the highest of his career. 

You can't even get a read on Hill by looking at his pitch type values. Those are valuations against various pitch types as compiled by Fangraphs (among others). Some years he's good against fastballs. Other years, he's terrible. Some years, he's good against curves. Other years he isn't and so on with every pitch type. Over the years, it seems he's had more success with the curve than against any other pitch type. Strange.

All these thoughts came about because this author was trying to decide if the Arizona Diamondbacks did a smart thing by signing Hill for two years at just above $10 million. The answer really becomes, "We'll have to wait and see." It could pay off big as Hill has compiled a value (per Fangraphs) of $58.4 million in seven years or an average of $8.4 million a season. That means that Hill has a lot of upside on making a little over $5 million a season. But it also seems a crap shoot because Hill's valuation through those years has been all over the place. 

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