Why are you using errors to determine how good a defender is? It's not perfect obviously but someone who is close to leading the league in errors for his position isn't having too good of a season. Lee has been good but to his normal level so far. I don't that's really true at all. All that means is he's botched a few routine plays. Routine plays don't make a defender great. The things that make Lee a great defender have still been there all season. Errors also could mean a defender botched a tough play that he made look easy. Perhaps an infielder has very good range and gets to a lot more balls than other defenders, so he gets more chances to botch plays.