This is now the third consecutive year in which I’ve written a post about the potential misuse of defensive metrics early in the season. We all want as large a sample size as possible to gather data and make sure what we are looking at is real. That is especially true with defensive statistics, which are reliable, but take longer than other stats to become so.
While the reminder is still a useful one, this year’s edition is a bit different. Past years have necessitated the publication of two posts on UZR outliers. This year, due to the lack of outliers at the moment, one post will be sufficient.
First, let’s begin with an excerpt from the UZR primer by Mitchel Lichtman:
Most of you are familiar with OPS, on base percentage plus slugging average. That is a very reliable metric even after one season of performance, or around 600 PA. In fact, the year-to-year correlation of OPS for full-time players, somewhat of a proxy for reliability, is almost .7. UZR, in contrast, depending on the position, has a year-to-year correlation of around .5. So a year of OPS data is roughly equivalent to a year and half to two years of UZR.
Last season, I identified 10 players whose defensive numbers one-third of the way into the season didn’t line up with their career numbers: six who were underperforming and four who were overperforming. The players in the table below were all at least six runs worse than their three-year averages from previous seasons. If they had kept that pace, they would have lost two WAR in one season just from defense alone. None of those six players kept that pace, and all improved their numbers over the course of the season.
2016 UZR Early Underperfomers
The next table depicts the guys who appeared to be overperforming early on. If these players were to keep pace with their early-season exploits, the rest-of-season column would be double the one-third column. Brandon Crawford actually came fairly close to reaching that mark; nobody else did, however, as the other three put up worse numbers over the last two-thirds of the season than they had in its first third.
2016 UZR Early Overperfomers
Just like with the underperfomers, all four of overperformers had recorded defensive marks six runs off their established levels. Replicating those figures over the rest of the season would have meant a two-win gain on defense alone. Again, no one accomplished that particular feat.
A funny thing happened when I ran the numbers for this season. There weren’t any outliers of a magnitude similar to last season or the season before. It’s possible you missed the announcement at the end of April, but there have been some changes made to UZR to help improve the metric.
Read the rest of this entry »