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Does The Green Monster Really Skew Fielding Statistics?

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[EDITOR'S NOTE: I wrote this post on Monday, before Ellsbury was officially the Red Sox's leftfielder. Instead of me hacking it to pieces, just keep that in mind.]

There's a lot of talk about moving Jacoby Ellsbury from center field to left field next season for the Red Sox. With sure-fielding Mike Cameron occupying a roster spot now, the Red Sox have two options: play Cameron in center and move Ellsbury, or keep Ellsbury in his center field spot and slide Cameron over.

The idea behind moving Ellsbury is that his defensive numbers would improve in left field because he has less area to cover because a) he's playing in front of the Monster and b) Cameron is rolling territory to his left.

But there's also the idea that playing in left field in Fenway skews defensive numbers because of the Monster. Since we can't really put a number to the difference between left field in Fenway and a left field in, say, Yankee Stadium, all we can really do is get a rough idea.

So, is there a significant difference?

I decided to look at all the UZR/150 data I could find going back for Red Sox left fielders. Unfortunately, since UZR/150 is a very new statistic, I could only go back until the 2002 season. Meaning we have two full-time left fielders to look at: Jason Bay and Manny Ramirez.

We'll start with Bay. Here's how his numbers look in his time in Fenway playing left field:

INN UZR/150
2009 1279.1 -11.2
2008 423.1 -24

Bay improved in his second year with the Sox. This could be for any number of reasons, but one reason may because he became more familiar with Fenway Park. Still, no matter how you slice it, Bay was a bad left fielder for the Sox in 2009.

Here are Manny's numbers with the Red Sox. I only used seasons in which Manny played the most games in left. In 2002, he played a chunk of games as the designated hitter, but he still played more games in left for the Sox than any other player:

INN UZR/150
2008 537.2 4.8
2007 994.2 -28.3
2006 1031.1 -24.2
2005 1225 -15.7
2004 1087.2 -9.3
2003 1073 11
2002 529.1 -15.6

Manny's UZR numbers fluctuate a tad at the beginning of his career with Boston. In 2002 in limited time, he really struggled. This could be to being unfamilar with the Monster. In 2003, his first full year in left, he put up really good UZR numbers. Maybe he was out to prove himself. But after that he was just on a horrible, horrible slide. His UZR/150 got worse and worse and worse and worse. Then, finally, in limited innings in 2008 he put up positive numbers. But does anyone else think that those numbers would drop if he had put in a full season in Boston?

What can we deduce from Bay's and Manny's numbers? They're both bad fielders. Does that tell us anything about Fenway Park? Not even close.

But let's see how these two guys perform when they're not in Fenway.

Bay playing in left field before he was a Red Sox:

INN UZR/150
2008 921.1 -14.4
2007 1237 -11.4
2006 1373 3
2005 1185 -4.4
2004 963 -7.2

Other than 2006, which is most certainly an outlier, Bay was just as bad with Pittsburgh as he was with the Red Sox. Last time I checked, though, PNC Park doesn't not have a Yellow Monster in left field.

Manny's numbers since he's been in L.A.:

INN UZR/150
2009 812 -15.4
2008 436.1 -12.8

More bad numbers from Manny. His time in Los Angeles hasn't created numbers as bad as his last two seasons in Boston, but run about par for the course for his entire Red Sox career.

Could his somewhat better numbers as a Dodger be because he got away from the Monster? It's possible, but there are too many factors involved to really say one way or another. If that was true, why would Manny go from a good UZR/150 before being traded from the Sox in 2008 to a horrible one with the Dodgers in the same year? Manny also had a lot to prove these last two seasons, one reason why he could go from a career-low -28.3 with the Sox to a -15.4 in 2009 with the Dodgers.

Perhaps it would be easier to tell how the Monster effects fielders if a) there is more data available and b) the Red Sox's left fielders in that time weren't so bad. Bad fielders tend to be bad everywhere they play. Average fielders could be above average in on park or below average in another.

Maybe we won't ever really know what Fenway does to left fielders' gloves. But we should all sleep easy tonight knowing that no matter who plays left field next season -- Cameron, Ellsbury or even Jeremy Hermida -- they all should be better than Bay or Manny. Because, well, that isn't a feat very hard to accomplish.