UZR Updates!

The first UZR updates of the 2010 season are in, and from here on out they’ll be updated every Sunday night.

There have been a few improvements made to UZR this year, which will also be reflected in prior year’s UZR data. The changes do impact a few players, but for the most part, each player’s UZR has remained unchanged or is within a couple runs of what a player was rated before the improvements. Mitchel Lichtman, the man behind UZR, outlines the changes below:

Park factors have been improved, especially for “quirky parks and portions of parks,” such as LF and CF at Fenway, LF in Houston, RF in the Metrodome, and the entire OF in Coors Field. Of course, park factors in general are updated every year, as we get more data in each park, and as new parks come into existence and old parks make material (to fielding) changes.

In the forthcoming UZR splits section, we will also be presenting UZR home and road splits, as a sanity check for those of you who are skeptical of park factors. Please keep in mind that regardless of the quality of the park adjustments, there can and will be substantial random fluctuations in the difference between home and away UZRs and it is best to evaluate a fielder based on as much data as possible (e.g., using home and road stats combined), as we do with most metrics and statistics.

Adjustments have been added to account for the power of the batter as a proxy for outfielder positioning, so that, for example, if an outfielder happened to have “faced” a disproportionate percentage of batters with less than or more than average power, the UZR calculations will make the appropriate adjustments (as best as it can). Obviously, these kinds of adjustments are more important for smaller samples of data than for larger samples, since, in larger samples, these kinds of anomalies (in terms of opponents faced) tend to “even out.”

For infielders, similar adjustments are made for the speed of the batter, as a proxy for infielder positioning and how quickly the infielders have to field and release the ball, as well as the speed of the throw.

When a “shift” is on in the infield, according to the BIS stringers, if the play was affected by the shift, the UZR engine ignores the play. As well, if an air ball hits the outfield wall and in the judgment of the BIS stringers, no outfielder could have caught the ball, the play is similarly ignored.

Also keep in mind that UZR does not include first basemen “scoops” or the ability of the first baseman to influence hits and errors caused by errant throws from the other infielders. According to my (MGL) research, yearly “scoops” numbers are generally in the 1-4 run range, which means that the true talent range of most first basemen with respect to “scoops” is probably in the plus or minus 2 runs per year range – i.e., not much.

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David Appelman is the creator of FanGraphs.

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