Over the last 10 years or so, the “advanced” statistics that became popular evaluated players against a position specific offensive baseline – VORP, for example. If a shortstop and a second baseman had the exact same batting line, the shortstop would rate higher by that kind of metric, due to the fact that second baseman hit better as a group than shortstops. As such, it’s become exceedingly common to see people write things like “he’s got enough offense to be valuable as a shortstop, but he doesn’t hit enough to play second or third”.
Positions are essentially just a way to arrange players in a manner that produces the most efficient defense possible. You can literally play anyone anywhere – there’s no rule preventing the Nationals from sticking Adam Dunn at shortstop, for instance. They realize, however, that they will field a better team by minimizing the amount of times that Dunn has to move laterally in order to make a play, so they hide him at first base.
I agree in heart with this post. However, I believe it misses a couple of crucial points. It does not take into account how a player can get used to his position, or how he can have a skill set that is more attuned to a position’s needs. For instance, a third baseman needs less lateral range than a second baseman, who in turn needs less back and forth range than a shortstop, and the defensive spectrum fails to recognize this. UZR is not perfect, and no measure but FieldFX ever will be. However, this is such an imperfect science, I don’t expect that we will ever be able to grasp all the nuances of defense.