It depends how Hoyer diagnoses his poor 2009 UZR in centerfield. The most plausible explanation I've heard so far (I can't remember the poster for sure; it may have been smastroyin) was that Ellsbury's newfound difficulties on balls coming in could best be explained by overcompensation for his earlier problems with the walls. In other words, he started playing deeper than he should have in order to have more time to gauge deep flyballs near the wall, which led in turn to more bloops dropping in front of him. That in turn led to Ellsbury distrusting his first instincts and getting slower breaks. As the season went on, he improved on deep flies, turning in some memorable warning track and against-the-wall catches, but deteriorated on short hits. Those are mindset issues, not physical limitations, and thus are more likely to be overcome. It's not certain, to be sure, since depth perception may be easier in the corner outfield spots when the batted ball tends to hook or slice, compared to balls hit at, but in front of the centerfielder. Ellsbury's special blind spot in 2009 seemed to be softly hit balls in short right-centerfield.
Also, Ellsbury's UZR needs to be adjusted for the Monster and the lower, but still high, centerfield wall. Wallballs against either wall count against the centerfielder as well as the leftfielder in Fenway in that they appear on paper to be in the fielder's zone and catchable, but aren't in reality.
Assuming that Hoyer saw the same things, he might think that Fenway was a problem for Ellsbury because of its confines, and that he would be a better fielder in larger parks where his speed could come more into play.
In the thread about the Dewan chat over on The Book Blog
, MGL said that he was going to change that wall ball factor like Dewan has already done. I'm not sure if he made the changes during the season or if he's making them this off-season. He went on to say that he already accounted for the Wall factor in Fenway somewhat with his park adjustments. He also said that the wild fluctuations from one year to the next could be due to a variety of factors, including measurement error. Here is a very small sample of his response along with a question before it about year to year fluctuations. I think the Ellsbury question is from our chat with Dewan:
Here is one question, or at least a similar one, which I hear/read probably a hundred times a year, more or less
What kinds of factors skew statistical analyses of defense?
I’ll give a concrete example: Jacoby Ellsbury’s defense has fallen off a cliff this year, according to most advanced metrics. I find it hard to believe that he was an elite defender in 2008 and is now a poor one. Can you make an educated guess whether one year’s rating is more likely to be an aberration than the other? If so, what factors would you look for as signs that a particular player’s rating is an aberration (or, inversely, is especially likely to be accurate)?
My response is very important because many people, even astute followers of sabermetric stats and principles, still do not get what it means to present a metric which represents a sample of a player’s performance, or I should say, a measurement of that performance (I qualified that because in addition to random fluctuation in the “value” of the performance, we also have random - or even biased - variation in the metric because of measurement error).Player A has a stellar UZR (or OPS, or lwts, or ERA, or FIP, or whatever) one year and then a really bad one the next year. Or vice versa. Player is not hurt in one of those years and healthy in the other, as far as we know. How can this be! Dial 911! How can a player be fantastic with the glove one year (say, according to UZR) and terrible the next year. That just can’t be! There must be something wrong with the metric!
Let me re-state the problem succintly:
When a player has a good or great UZR in any time period, it does NOT mean that he is a good or great player and it does not even mean that he had a good or great year with the glove. What does it mean, you ask? Well, it doesn’t mean anything other than he had a good or great UZR. It really doesn’t. He may be a bad or average defensive player who had a good 147 games with the glove (woop-de-do_. It may be a bad or average defensive player who did NOT have a good or great year with the glove but the way we measure defense with UZR just got it wrong.