Joe Posnanski speculated on the differences in a recent article about Josh Hamilton’s MVP chances:
*I could be reading this wrong, but Fangraphs seems to put more emphasis on defense. For instance, Carl Crawford’s WAR at Baseball Reference is 3.7 — his defense is worth eight runs above average. But Fangraphs credits him for 22 runs above average, which thrusts his WAR up to 5.6 and into the No. 4 spot in baseball.
I’ve seen similar sentiments echoed throughout the blogosphere and on Twitter.
In reality, on a per-player basis in 2009, UZR distributed 441 fewer runs than TZ did, excluding pitchers and catchers. And there is not a year that UZR is available where its absolute value has been higher than TZ.
In 2009, the maximum spread of UZR was +31 to -37 and TZ showed a similar spread of +31 to -34. Here’s a graph of the full spread. The blue overlap shows the points at which TZ starts showing a greater spread.
This might not be a perfect comparison in how much defense actually contributes to WAR and a better one might be how much as a whole does fielding contribute to total runs. In 2009, fielding made up about 14.2% of all positive and negative runs according to FanGraphs WAR, while Rally’s WAR made up about 15.5% of all positive and negative runs.
All in all, they are similar in how fielding is weighted as a whole. The biggest difference between the two is how each individual player’s fielding is evaluated.