Defensive Stats In The Times
This got lost in the shuffle with all of yesterday’s news, but Baker wrote a long story on defensive statistics and their use in evaluating fielding prowess. If you haven’t read it, it’s worth checking out.
Baker did a ton of work on this piece. He spent 45 minutes on the phone with me, and I’m a sidebar to the real story. He also talked to Dewan, Lichtman, and Blengino, and he made sure he had as much information as he could get. He does a pretty good job giving an overview of what +/-/UZR/PMR do without making the barrier for reading the article too high. It’s certainly an entry level piece, but that’s where 99 % of the Times readers are at.
Baker also wrote a supplemental blog post where he adds a little context to the article, explaining that he just didn’t have the space to fit in every angle. Defensive statistics are complicated, and he’s right – you just can’t sum them up in 2,000 words without leaving out a lot of stuff.
One of the things I told Geoff in our phone conversation is that I tend to look at the advanced defensive statistics much like ERA. ERA measures pitching ability, teammates fielding ability, scorer bias, park effects, and luck. It includes a bunch of stuff that pitchers have no control over, but most casual fans have no problem accetping ERA as a measure of pitcher value. Likewise, UZR and +/- measure range and instincts, but also positioning (is that the player or the coach?), pitchers ability (not all balls in play are equally catchable), scorer bias (line drive or fly ball?), park effects (do fly balls in Safeco’s LF hang up longer than in other parks?), and luck (did you get a bunch of weakly hit ground balls that were easier plays that they looked on paper?).
We’ve moved beyond ERA for evaluating pitchers because we have better metrics now – things like FIP strip out a lot of the non-pitcher stuff and give us a better tool for just evaluating the pitching aspect of run prevention. We’ll have better things than current UZR and +/- shortly, once Hit F/x is introduced and we have speed/trajectory/hang time of batted balls. But, until then, UZR and +/- are better than anything else out there right now, and they’re good enough as long as the issues with the stats are accounted for.
The shortcomings that Baker (and Ibanez) point to are real, and that’s why we talk about players fielding in terms of ranges. We say that a guy is a +10 to +20 fielder, for instance, and we won’t argue any number in that interval. He might be +11 or +19 – we’re not sure. There’s noise in the data. We know that, and we account for it.
Do you ever hear people do this with ERA, though? The same noise (probably more, actually) exists in ERA, but you never hear someone say that a pitcher is a 4.25 to 4.75 ERA guy. They’ll say he has a 4.36 ERA, and that’s what’s used to evaluate his past performance – the noise is ignored and the entirety of the number is attributed to the pitcher.
In most ways, I think people like us who are pushing the value of advanced defensive metrics have been far more honest about the quality of the metrics we’re using than those who reject our numbers as not good enough but cling to Batting Average, RBIs, and ERA.
Current advanced fielding data, such as UZR, should be looked at much like you do ERA. It’s got some problems, no doubt, but we don’t have a FIP for fielding just yet, so until we do, it’s a good enough proxy if you acknowledge the flaws. We’ll have a FIP-like fielding metric soon enough. Until then, UZR is better than anything else out there, and using it to make decisions will lead to more correct decisions than ignoring it entirely.