Just plain old UZR, with quick looks at a few other metrics to make sure they're in relative agreement. And to answer your question, generally speaking you'll see a bit less deviation when you're looking at middle infielders. That makes sense of course, considering they are defense-first positions. But even at that, a few players were pretty bad this season. Dan Uggla and Luis Castillo were about 10 runs below average, Miguel Tejada and Orlando Cabrera around 15 and Yuniesky Betancourt just over 20 runs below average. Of course, there are other factors that enter into play. Middle infielders do get quite a few more chances... but their failures don't generally end up as disastrous as those in the outfield. But what about things like extended innings? Extra outs? Extra hits? With a small outfield like Wrigley and the nature of the position, I can't see a good defensive RF being worth more than a good defensive SS, even if he would botch a flyball or two every month. Except that the errors are the smallest part of Dye's problem. If he can get to the ball, he's not far below average at all. Likewise, his arm isn't doing an adequate job, but the arm and the extra errors only account for about 3 and a half runs below average... far from disastrous. His range is the issue. Every ball hit into the gap or up the line that good RF like Ichiro or Justin Upton catches but Dye doesn't is 2-3 bases for the batter and every runner on base. It adds up very, very quickly. Could a park adjustment make a difference? Sure. Will it make enough of one to make him a valuable player? No. Last season, Jermaine Dye's production was actually worth about $1.2 million dollars less than you could expect from a replacement level player. This is the second time in the last three seasons that he's been below replacement level. Could he bounce back to his 2008 level of offensive production and be worth a few million bucks? Sure. But at his age, it's not a terribly likely proposition.