Okay, so, Derek beat me to the announcement that we’ve started carrying UZR data over at FanGraphs. It’s pretty awesome, and hopefully, if you’re not already reading FanGraphs every day, you will start.
Leading up to the launch, I wrote a few articles about understanding defensive statistics and practically applying them. Not to be too self promoting, but I think you should read those. Defensive statistics cannot be viewed the same way as offensive statistics, and I try to make that clear in those posts.
For instance, in the comments of the last two sections, we’re seeing a lot of stuff that refers to Betancourt as “the worst defensive infielder” because his UZR/150 was -14.7 last year. However, you simply can’t make a claim like that. Here’s why:
1. UZR had Betancourt at -15 runs below an average shortstop in 2008. Shortstops are far and away the best defensive players in the game. His peer group is great defenders, which is just not true for 2B, 3B, or especially 1B. A -15 mark at SS is not the same thing as a -15 mark at another position.
2. Sample size – you cannot make concrete statements about a player’s true talent defensive level based on one season’s worth of data. Realistically, you need about 2,000 to 3,000 innings to eliminate enough of the variance to make a good judgment call. On it’s own, Betancourt’s -14.7 doesn’t mean an awful lot, and it certainly can’t be stated that he’s definitely the worst defensive SS in the game. He’s almost certainly below average, and he did have a poor defensive season last year, but don’t get carried away with valuing players based on a single season’s rating.
The fact that we have publicly available UZR data is a huge breakthrough, but please, use the data properly.