For fielding, I have used MGL's UZR, which can be found here. UZR is just one of many fielding metrics, but it is thought to be pretty accurate, and is released intermittently throughout the season.
First, the current top ten in adjusted WPA:
This is where Jeter reaps the benefits of his position, ad he moves from fourth in WPA to second in adjusted WPA. Unfortunately, you have to actually play defense. Which brings us to fielding, and the top 10 in UZR:
Some other notables:
Combining the two (and dividing UZR by 10, as 10 runs is about equal to one win, we get the ten most valuable players thus far:
A-Rod has what is probably an insurmountable lead. Even if Jeter played defense like Adam Everett (UZR of 11), he would only be in second (.6 behind Rodriguez). And his defense is much closer to Manny (-14) than Everett.
Sizemore's position and unbelievable defense allow him to vault from ninth in straight WPA to third in my rankings.
Unfortunately, there is no UZR for catchers, which is why Martinez and Posada have UZRs of 0. I found it interesting that the league's two top hitters (Magglio and A-Rod) both play outstanding defense.NL MVP Watch is now up.