Over at Baseball Musings, David Pinto has posted the "Probabilistic Model of Range, Third Basemen". I was surprised to see that Melvin Mora was toward the top of the list. (Range refers to the percentage of plays that a fielder *should* have made. David's way of determining range is not the same as other measures of the skill.)
I recall that when David did his range rankings for shortsops that Miguel Tejada, that Tejada didn't come out so well. This was also a surprise.
It's also worth noting that for the Yankees, A-Rod, the 3rd baseman did well the shortstop Jeter, did not.
A-Rod and Mora have something in common: They're both ex- shortstops. (Though it's been awhile since Melvin played shortstop.) I'm wondering if there's an aggressiveness that shortstops have that third basemen don't usually have. So both of them got to balls to their left, that normally would have shortstop plays thus increasing their range and decreasing the range of their shortstops? (Or maybe generally, shortstops are quicker than 3rd basemen.)
I realize two players constitute a very small sample size, so it may be impossible to draw any conclusions here.