Defense could cost Minnesota Twins

Alexi Casilla is a bit of an unknown in the field, but he'll struggle to match J.J. Hardy's 8.1 UZR. Otto Greule Jr./Getty Images

The Minnesota Twins have taken plenty of flak for the mass exodus from their bullpen and their many unproven, younger relievers. But the Twins have a much bigger problem on their hands for 2011, one that could threaten their two-year reign as AL Central champs: a severely diminished defense.

The Twins finished sixth in team ultimate zone rating last season. Developed by Mitchel Lichtman and tracked by FanGraphs, UZR is a stat that measures the number of runs a player saves compared to the average player at his position. It's more reliable on a three-year basis, though, and at times subject to small-sample-size flukes, such as Jason Repko's team-leading performance in just 58 games played.

Random fluctuations aside, the Twins' biggest defensive downgrade this season comes at shortstop, where Alexi Casilla takes over for J.J. Hardy. Per UZR, we see that Hardy ranked among the Twins' best defenders last season. He earned a UZR of 8.1 in 2010, saving just more than eight runs last year as compared to an average defensive shortstop. And this wasn't a one-year fluke. For his career, Hardy has a UZR of 11.0 per 150 games played. Using the sabermetric convention of 10 runs saved equaling one win gained in the standings, that means Hardy is worth one full win more than an average shortstop each year with his glove alone.