Dewan +/- has him at -75 basic for his career and -147 enhanced for his career

Fangraphs has his UZR at -66

Baseball-Reference has his Total Zone at -5.5

Baseball Prospectus has him at -33.8 Field Runs Against Average

2013 Scouting Report:

"As a defender, I’ve never thought he was playing his true position. He’s just fair, at best, in center. But by putting him in center, what are you getting in the corners? Are you getting an extra 30 or 40 more runs on the field offensively, compared to the 20 or 30 you’re giving up by having a less-than-great defender in center? With both Kemp and Ethier, you don’t hear, “Gold Glove defender,” very often any more. I’ve never made a report where I’ve written that on either of them."

Going by any conceivable objective measurement, he's bad.

But, yeah that was a nice catch tonight.