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# Fun with Defensive Data, or FanGraphs is Awesome

Already a veritable Willy Wonka wonderland for us sabermetric chocoholics, FanGraphs somehow keeps finding ways to get more and more delectable. A week or so ago, they added the Fielding Bible defensive numbers to their site, providing us with yet another freely available metric to use when analyzing fielding. We all know and love UZR (Ultimate Zone Rating), but the Dewan Plus-Minus systems is widely considered to be one of the best defensive metrics as well. Up until now these numbers were only available in John Dewan's yearly publication "The Fielding Bible" (which was the main reason we used UZR and not Plus-Minus - ease of access), but now we can use them all year long. These statistics (along with UZR) will be updated periodically as the season progresses.

For those of you unfamiliar with the Dewan Plus-Minus system, please feel free to drop by the Sabermetric Library and acquaint yourself with the metric. My favorite explanation of the stat (and the one I use at the Library) comes from Joe Posnanski:

"My go-to defensive statistic, this was invented by John Dewan, and it as I understand it, the numbers determines (using film study and computer comparisons) how many more or fewer successful plays a defensive player will make than league average. For instance, if a shortstop makes a play that only 24% of shortstops make, he will get .76 of a point (1 full point mine .24). If a shortstop BLOWS a play that 82% of shortstops make, then you subtract .82 of a point. And at the end, you add it all up and get a plus/minus."

I'm not going to get into the technical similarities and differences between UZR and the Dewan system; I'll leave that up to people much smarter than me (like herehere, and here). Here's what you need to know for how we'll use the statistic on the site:

1. The Fielding Bible statistics available on FanGraphs are all available in runs form instead of plays. Joe Poz's description above is right on just that instead of measuring a player's plays above or below average, FanGraphs displays the stats as runs above or below average. Since UZR is displayed as runs above or below average, this means we can compare apples to oranges. Make sense?
2. The Fielding Bible equivalent to UZR (meaning the statistic that measures how many total runs above or below average a player is on defense) is Defensive Runs Saved (DRS). Remember that acronym and get used to it.
3. Most players will have very similar UZR and DRS scores. Although there are normally one or two players that UZR and DRS don't agree on, the vast majority of players will have scores within a couple runs of each other. For example, Evan Longoria had a 17 DRS last season and a 18.1 UZR.
4. DRS provides us without another statistic to use to quantify a player's defense, which can be very useful since defensive data is not as reliable as other statistics. Take Mark Teixeira as an example. Many people believe that he is an elite defensive first baseman, but he posted a pedestrian 0.1 UZR last season, leading many people to believe that the statistic was faulty. "Oh, defensive data is so unreliable, we can ignore that and believe that he had a great defensive year anyway." While that's true to a point (yes, he probably is still an above-average fielder), DRS also showed Teixeira putting up a ho-hum season last year (-1 DRS). Since both these statistics agree, it seems likely that Teixeira had a down year defensively last season. In other words, this metric gives us something with which to double-check UZR scores.

For your viewing pleasure, here are the Rays' 2009 UZR and DRS scores:

 DRS UZR Evan Longoria 17 18.1 Carl Crawford 24 17.6 Ben Zobrist 12 12.3 Ben Zobrist 18 11.7 Gabe Kapler 6 7 B.J. Upton 3 6.8 Gabe Gross 8 5.5 Reid Brignac -1 -1.4 Willy Aybar -3 -2.3 Akinori Iwamura 2 -3.4 Jason Bartlett 4 -3.5 Carlos Pena -6 -4.7