Posted by Sean Forman on September 6, 2011
I'm not going to speak to the larger discussion around this article because the author loses a lot of credibility/weight (at least for me) when he admits in the comments, "I slightly misrepresent how the stat works here, in favor of making the statement more hyperbolic." That and the article is being discussed elsewhere, but one of the comments points out a particular issue that annoys me.
Here is the Comment by Hank
I'll post this again....
Carl Crawford career LF at the Trop 22.5 UZR/150
Carl Crawford career LF everywhere else: 7.5 UZR/150
This is over 8 years (so each sample size is the rough equivalent of 4 full years).
1 year OF UZR samples are bad, but even the general "3 years is what you need" can also have issue as UZR can have systematic biases.... input bias, park effects and subjective components (armR, errR for outfielders) which don't even out over a 3 year period.
I like the concept of WAR and the issue I have with it is bad input data (the defensive stats in both WAR models and the baserunning values now put into the fWAR). Until these variables can be measured better (FieldFX?), any difference in WAR between players based on these components should be taken with a huge boulder of salt.
OR ANOTHER OF A SIMILAR VEIN
THANK YOU for this post.
UZR may be good for multiple years, but it is a flawed single season stat. Saying Carl Crawford one year in TB went from being an elite LF to being a terrible one the next year makes no sense.
What is the issue here exactly? Why would a difference in home and road UZR be evidence of a flaw in UZR? Or why would the fact that Crawford's UZR is much worse this year mean there is a problem with uzr? Some players hit a lot better at home than on the road? Why wouldn't fielders see the same effect.
For some reason when defensive numbers are inconsistent across splits or years folks gnash their teeth and blame the faulty defensive metrics, but Carl Crawford can go from an OPS+ of 135 to 82 in a year and people won't question the offensive numbers.
Why do we expect greater consistency on defense than on offense? That doesn't seem to me to be a valid expectation.