Since this is being discussed in numerous threads, I figured this would be a good time to start an overall UZR thread.
Clearly there is a strong disagreement over UZR and how it should be used, especially itís place in fWAR. I think itís a huge improvement over previous attempts evaluate defense production and skill level, but it still has major problems. Here are what I think are the major problems with UZR. These are just opinions and I welcome anyone to show me where I am wrong:
1. This has been discussed before, but UZR doesnít take into account positioning. As we have all seen, fielders positioned properly in regards to where the hitter is likely to hit the ball, save plenty of hits and runs. But UZR ignores these.
A player who starts the play out of his normal position, and easily makes the play because of it, saves a hit, but UZR counts it a ball in his zone, since they count where the fielder starts in determining what a normal zone is for him, not where he would normally play. If he had started where he normally plays, the ball is either a hit, or he catches it out of his zone, and he get credit for an out of the zone play. Either way, heís penalized for positioning himself properly.
2. Arm rating. This is only used in the outfield, and it penalizes veteran fielders with strong arms and over benefits most new fielders with even decent arms. Veterans with strong arms, almost never get run on. Which means they donít get many assists. UZR doesnít give a point to OFís who prevented runners from taking extra bases with the fear of his arm. Yet that happens far more often than an OF who nails a runner taking an extra base.
With most new OFís , runners are more likely to run on them, as no one knows exactly how strong their arms are. Therefore, new OFís get many more assists in their first season than they do afterwards, and therefore, in their first season, they get a much higher arm rating than they deserve.
3. This one Iím not so sure about but I think Iím right about it. UZR gives double points to fielders in valuable positions who have above average range. For instance, SS already get around 6 extra runs added to their WAR, simply for playing SS. I get why, since their UZR is a number that compares them to other SS, so the extra value of being a SS needs to be added.
But the reason why SS are more valuable than say, a 3B, is that SS get more balls hit in and around their zone. Which means that a SS with above average range, will get more chances to make plays out of his zone than a 3B with the same range. A SS gets around 32 more balls hit out of his zone than a 3B, according to my attempt at math and Fangraphs. Which makes sense, since his zone is bigger, a 3B can only go out his zone to his left, back and in, while a SS can go a full circle out of his zone. If both fielders get to 25% more balls out of their zone, the SS will get 8 more balls out of his zone, with the same skill level. Thatís almost a run different. So SS with above average range, will have a higher UZR and WAR than a similarly skilled 3B.