Thanks to Charlie at Bucs Dugout for this one.
The Baseball Analysts attempt to quantify minor league defensive numbers from play-by-play data. Charlie notes the errors that could happen in a study like this, but, as he says, it's nice someone is giving it a try.
And take a look at the best defensive shortstops in the minor leagues. No. 7 and No. 8 are Pirate prospects, Brent Lillibridge and Brian Bixler, respectively.