Inspired by Escobar's crappy UZR this season as mentioned in the FanShot section by JKWard, I decided to write out one of my grievances with what I understand as how the two major advanced defensive metrics handle defensive positioning. My understanding might be completely wrong, but from what I've read describing their methods, I think it's fair to say that I don't like how either system handles "shifts."
A player's defensive positioning before a pitch is variable, and the team should make an effort to optimize positioning according to the batter's tendencies, the pitcher's tendencies, and the pitch type that will be thrown. If you measure down to the inch, there are literally hundreds of thousands of positions that a shortstop could reasonably stand before a pitch.
But UZR handles "shifts" as an on-off switch; the player is either shifted or he isn't. If UZR deems that a shift is on, the play doesn't count for UZR's tabulations. If they determine that a shift is not on, the player will be scored as though he were standing in the middle of his position's defensive zone, regardless of where he's actually standing.
DRS has an even less complicated system. Their calculations don't care at all where a player is standing--the player will always be scored as though he were standing smack-dab in the center of where the league usually sets up to play his position. The third baseman can literally be shifted to stand behind the hole between the first baseman and the second baseman, and DRS will score the play as though he were standing at third base. The Blue Jays actually employ this shift reguarly, so Brett Lawrie has some incredibly rangey plays to his left according to DRS.
Neither system makes much sense, and the problem is getting worse as teams are expending more effort to optimize their defensive positioning. The Royals tend to put a traditional exaggerated shift where the SS stands right behind second base against LHB's with pull-tendencies, but they also shift toward the 3B line against RHB's with pull-tendencies. I believe UZR ignores plays of the first type, calling them "shifts," but scores the second type of play as though the positioning were totally normal.
This asymmetry in scoring policy where UZR counts the plays where the defense is shifted toward the 3B line but discounts the plays where the defense is shifted toward the 1B line not should, over time, make Escobar's range to his right look a little better and his range to his left look worse. It has the potential to artificially deflate Escobar's overall UZR if balls are going for hits through the normal SS zone but out of Escobar's possible range since he's standing closer to the third baseman's territory. (It's worth noting that in these shifts, Escobar is at least partially receiving credit/blame for the second baseman's defensive performance since the second baseman should be able to reach part of the SS's zone. It's also worth noting that Yuniesky Betancourt was the second baseman for many of Escobar's games in 2012.)
The scoring asymmetry also has the potential to artificially inflate Moustakas's overall UZR if he's gobbling up balls down the 3B line, and Escobar is there to field the balls that Moose misses to his left.