Wednesday, January 03, 2007

Davenport's Fielding Translations

In an earlier article, I discussed Chris Dial's translation of zone rating into runs saved above average (RSAA). Another statistic which is used to quantify fielding performance in terms of runs scored is Fielding Runs Above Average (FRAA). FRAA is the creation of Clay Davenport who does research for Baseball Prospectus. FRAA and the other Davenport Fielding Stats are often referred to collectively as Davenport's Fielding Translations (DFT).

There does not seem to be a detailed explanation of the DFT algorithm on the BP site but my understanding is that it is somewhat similar to Bill James' Relative Range statistic introduced in last year's Fielding Bible It takes a fielder's range factor and makes adjustments for innings played, team defense, estimated ground ball/fly ball data, strike outs and some other things. It then compares the range to league average and estimates the number of runs saved above or below average.

The drawback of DFT is that the method is proprietary so we don't know all the details. It is believed to be the best fielding performance algorithm not based on play by play data. For years in which play by play data is available, DFT is not likely quite as accurate as play by play methods (like zone rating and PMR) . It is, however, believed to be the best method for evaluating players throughout the history of the game. It's also available year round on the BP web site and it's free at this time.

Table 1 compares Dial's RSAA to DFT FRAA for Tiger fielders in 2006. Right away, you'll notice some discrepancies between the two methods. For example, Carlos Guillen is 2 runs above average on the former and -13 below average on the latter. On the other hand, Curtis Granderson rates worse on Dial's RSAA (5) than he does on DFT (18).

One lesson to be learned here is that different fielding algorithms rank players somewhat differently. Because of this, it's good to use more than one method when trying to evaluate fielders. I do find that the really good fielders (such as Granderson, Brandon Inge and Placido Polanco) typically do well on all methods. In the next few weeks, I'll talk more about the use of multiple fielding measures and how they can be aggregated.


Table 1: Dial's RSAA Vs. DFT FRAA for Tigers in 2006

Position

Player

RSAA

DFT FRAA

1B

Casey

4

15

1B

Shelton

12

-2

2B

Polanco

14

6

3B

Inge

20

21

SS

Guillen

2

-13

LF

Monroe

1

-1

CF

Granderson

5

18

RF

Ordonez

-2

-4

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