What happened to Damon’s defense?

In 2007, Johnny Damon’s UZR in left was 7.5. In 2008, his UZR was 6.7 and his range, which is one of three defensive components included in one’s UZR, was actually better than it was in 2007. However, this season the valuable defensive player that Damon was only a year ago has failed to materialize. Damon’s UZR is -9.4 and his range is non-existent. He has suddenly become a liability rather than an asset to the team. In fact, Damon’s UZR has him ranked as the worst defensive left fielder in all of baseball (with regular playing time).

This development is strange considering his strong play there in past seasons and I’m not sure why there has been such a dramatic shift in Damon’s rating. Could he simply be having a bad year or is he feeling the effects of age and injury, specifically leg problems, in 2009? Also, while I’m not sure as to how accurate the following thought may be since I’m not the biggest statistical guy, I wonder if this year’s UZR in LF is measured differently when compared to last year’s figures.

UZR is defined as the “number of runs above or below average a fielder is in both range runs, outfield arm runs, double play runs and error runs combined.” This year, with defensive whiz kids like Nyjer Morgan, David DeJesus, Juan Rivera, and Juan Pierre playing LF—none of them were there much in 2008—the defense at that position has improved considerably (plus, guys like Dunn, Burrell and Manny haven’t played there much this season). Therefore, maybe what was once average in 2008 is no longer average in 2009 and Damon is being held to a higher standard. Of course, I don’t think this shift in “average-ness” would entirely account for his poor 2009 as he probably has regressed a good amount out in LF, but I do think it helps to understand the dramatic drop-off that has been captured in his UZR.

What do you think? And for the stat-heads, does that UZR theory make any sense or am I way off base (I apologize if that’s the case)?