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Posted By Steve Slowinski On February 15, 2010 @ 1:09 am In | 7 Comments

Ultimate Zone Rating (UZR) is one of the most widely used, publicly available defensive statistics. The theory behind UZR is tougher to intuitively grasp than Defensive Runs Saved (DRS), but the simplified version is that UZR puts a run value to defense, attempting to quantify how many runs a player saved or gave up through their fielding prowess (or lack thereof). There are a couple different components to UZR, including:

● Outfield Arm Runs (ARM) – The amount of runs above average an outfielder saves with their arm by preventing runners to advance.
● Double-Play Runs (DPR) – The amount of runs above average an infielder is in turning double-plays.
● Range Runs  (RngR) – Is the player an Ozzie Smith or an Adam Dunn? Do they get to more balls than average or not?
● Error Runs (ErrR) – Does the player commit more or fewer errors compared with a league-average player at their position?

The run values in each of these categories are then compiled into one overall defensive score, UZR. Since UZR is measured in runs, it can be compared easily with a player’s offensive contributions (wRAA).

For the details on how UZR is calculated — i.e. how we can attach a run value to defensive events — see the FanGraphs UZR Primer.


Since defensive statistics are still relatively new, they should not be taken as 100% dead accurate. Before drawing any conclusions about a player’s defense, look at a full three years of defensive data, drop the decimal points and take an average, and compare UZR scores with other defensive metrics (DRS, TZL, etc.). By taking a broader picture, you will help ensure that you’re not being over-confident or overstating a player’s defensive abilities.

In general, UZR scores can be broken down into the following tiers. This is a good shorthand way of evaluating a player’s defensive ability level:

Defensive Ability UZR
Gold Glove Caliber +15
Great +10
Above Average +5
Average  0
Below Average -5
Poor -10
Awful -15

Things to Remember:

● Beware of sample sizes! If a player only spent 50 innings at a position last season, it’d be a good idea not to draw too many conclusions from their UZR score over that time. Like with any defensive statistic, you should always use three years of UZR data before trying to draw any conclusions on the true talent level of a fielder.

● UZR uses Baseball Info Solutions (BIS) data in calculating its results. It’s important to note that this data is compiled by human scorers, which means that it likely includes some human error. Until FIELDF/x data gets released to the public, we are never going to have wholly accurate defensive data; human error is impossible to avoid when recording fielding locations by hand, no matter how meticulous the scorers. That said, BIS data is still the best, most accurate defensive data available at this time, so just be careful not to overstate claims of a player’s defensive prowess based solely on defensive stats.

● Since UZR is a counting statistic like RBIs or HRs, the more playing time a player accrues, the higher (or lower) their UZR will be. In order to compare players with different amounts of playing time, UZR can be  scaled on a 150 game basis (UZR/150). If you want to compare a player with 90 games played to someone with 140, UZR/150 would be the way to do so.

● UZR is park-adjusted, meaning it adjusts for the fact that fielders have to deal with odd quirks in certain ballparks.

Links for Further Reading:

Intro to UZR – Big League Stew

The Mike Silva Chronicles: UZR – The Book Blog

Similarities and Differences: UZR and Dewan +/-

Background to UZR, Pt. 1 – Baseball Think Factory

Background to UZR, Pt. 2 – Baseball Think Factory

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