Rob Neyer: Explaining some new math

As you know, I’ve been wrestling with this notion of positional adjustments, which on Thursday led to the following e-mail exchange with FanGraphs’ Eric Seidman …

Eric: Rob, I thought I would try to see if I could clarify the adjustments for you. Basically, it is all due to defense. Tom Tango likes to refer to the adjustments as “Runs Over Willie” (in honor of Willie Bloomquist, who can play everywhere). Essentially, the idea is that if you took Willie Bloomquist and put him anywhere on the field, what would an average fielder produce, runs-wise, compared to his production?

So, if you put Willie at 1B, the average 1B would cost his team 12.5 runs more than Willie. If you put Willie at shortstop, the average SS would save 7.5 runs more than Willie.

It’s really just a quantifiable way of showing which positions are the toughest to play. Catcher gets +12.5 runs because not everyone can play there. Shortstop gets +7.5 runs because it is the toughest non-catching position. Then comes 2B/3B/CF, at +2.5 runs apiece. LF/RF are docked -7.5 runs, and 1B docked -12.5 runs. Using these adjustments allows us to compare Carl Crawford in LF to Chase Utley at 2B.

If Crawford is +15 runs via UZR and Utley is +19 runs, it really isn’t as close as it seems, given that LF are docked -7.5 runs and 2B gain +2.5 runs. Before even factoring in offensive contribution or adding two wins (20 runs) to be above replacement level, Utley would be a +21.5 run defender, Crawford a +7.5 run defender.

Hope that makes some more sense. It is a very confusing concept, but basically it just allows us to make cross-positional comparisons so someone like Crawford doesn’t have an overstated defensive value.

Me: Is this a new thing? I don’t recall seeing any discussion of positional adjustments before the last couple of weeks. I’m just wondering if everything we thought we knew about player valuations have been wrong. Is Dave Concepcion worth more than we thought? Tony Perez less?

Eric: I wouldn’t necessarily call it two weeks new, but definitely new in the last year or two, as far as I know. Granted, I didn’t really “come onto the scene” until May 2007, but I can recall as far back as June 2007 reading Tango’s positional adjustment work.

I don’t think it means that everything we have already done is wrong, per se, because defensive stats weren’t really ever taken into account outside of Fielding Percentage for the longest time.

Huh, I didn’t realize that positional adjustments is considered so ‘new’.