Ultimate Zone Rating is a tricky calculation

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Wednesday, March 31, 2010

So how does one arrive at a player's Ultimate Zone Rating? Well, by far the easiest way is to let sabermetricians, such as those at the Web site http://fangraphs.com, do the hard work for you. But here is as simple an explanation as we can manage of the process that results in UZR.

First, take one ballpark, and dice it. Actually, sabermetricians use a standard model for all baseball fields, then they slice that into 78 zones. Partly because all real ballparks have different dimensions, they use only 64 of these zones in their calculations. Each position is considered responsible for a few of those zones.

The next step is to take the total number of balls put into play into each zone and divide it by the total number of outs recorded in each zone (with some modifications), thereby getting a league average. Then one does the same on an individual basis, looking at a given player's rate of recording outs on balls hit into zones that are considered his responsibility. If that player's rate is higher than the league average, he will have a positive (i.e., good) UZR.

But -- and you knew it couldn't be as relatively simple as that, right? -- that's not all that goes into UZR. Because, for one thing, ballparks not only have different dimensions but different surfaces, too, which can affect fielders' abilities to get to balls. So that's put into context.

Also, what if one right fielder has to handle an overabundance of screaming line drives into his area, while another right fielder seems to subsist solely on cans of corn? Believe it or not, there are people at every baseball game whose task it is to judge the power of every ball put into play, so those details get thrown into the mix.

And you had better believe that, for every ball put into play, it matters whether the batter was a lefty or righty. Just as it is important to note whether the pitcher was a ground-ball or fly-ball type. Same with the number of base runners and outs.

Oh, and there's always the tricky matter of errors, both those made by the fielder and the players at the other end of his throws. Oof, so many factors! But fear not, for we are blessed with an intrepid -- some might say clinically insane -- band of sabermetricians more than happy to wade into those murky waters and emerge with a meaningful statistic for a crucial but traditionally hard-to-quantify aspect of baseball.

-- Desmond Bieler


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