For those of you who want an inside look at some of the things that go into Ultimate Zone Rating, here's your chance. Take a look at this interview from Baseball Digest Daily:
Mitchel Lichtman (MGL): Thanks for asking. Being an analyst and not generally a promoter, I love these kinds of questions, rather than, "What do you think of the stats v. scouts debate?" or some such thing.
Actually, for a great description of UZR, read Dewan's Fielding Bible. They use essentially the same methodology.
UZR uses a STATS Inc. database, rather than BIS, although I assume that the databases are very similar; at least they should be. I break the field down into "grids" or zones, much smaller than the zones that STATS uses for its zone ratings, based upon distance and location. The location is a "pie slice" from foul line to foul line, with 22 slices across the field, each one around 4 degrees wide of course. John uses vectors and distance I believe, essentially an x. y coordinate on the field, for where an air ball lands or is caught or where a ground ball is caught or goes through the infield. Although STATS provides an x, y coordinate as well (from video also) in its data, I don't like to use data that granular, as the sample sizes will be too small to generate a meaningful baseline probability of a ball being caught, unless you use a function to smooth out the data.
Certainly interesting, and well worth the read.