In the realm of baseball statistics, there aren’t very many metrics that deal with defense. There are even less good ones. The best, so far, is UZR (Ultimate Zone Rating). UZR is expressed as runs earned or lost on defense. For example, if player X had a UZR of 10 in 2009, he would be worth 10 runs above average. UZR can also be expressed as a negative, something Adam Dunn is very familiar with.

UZR is somewhat complex, but I’ll give you the basic rundown.  UZR uses 64 of the 78 zones shown here. A computer keeps track of the number of hits in each zone, the average run value of a hit in that zone based on linear weights (same thing that wOBA uses), and the number of outs recorded in that zone for each position (some zones are shared by multiple defenders).

UZR determines the value of each zone, individually for each player and then totals all of the zones. The values of each zone are determined by using the league average data for each zone to compare to the player being studied.

UZR is far superior to fielding percentage, because it has a component that includes a player’s range. Fielding percentage is based off of a system of subjective official scorers who aren’t exactly consistent with their rulings and it fails to account for balls players can’t get to that others can.