Your immediate reaction to the news that the St. Louis Cardinals were an interested party in the trade rumors surrounding Cleveland Indians shortstop Asdrubal Cabrera was probably dependent on which website you trust for your WAR defense fix. Baseball Reference? Pretty psyched—he's got 17 career WAR, including two seasons with at least four, an All-Star level. FanGraphs? 13, including three seasons at three, which is above average.
The difference? FanGraphs relies on UZR (Ultimate Zone Rating), Mitchel Lichtman's influential formulation, while Baseball Reference's WAR uses DRS (Defensive Runs Saved), John Dewan's Fielding Bible metric. Most of the time these two ways of measuring a defender's range get along pretty well, but for Cabrera it's the difference between being an average shortstop (and a good second baseman) and being a mess.
So which will the Cardinals believe? Well, probably their own—Mitchel Licthman was a statistical analyst for the Cardinals, for a while, but I'm sure most teams have proprietary defensive metrics (and information) at this point. The circumstantial evidence goes both ways; he's a flashy defender who makes highlight reel plays, but he's also periodically chided for his weight, and his ability to stay in shape.
So, is Cabrera an average shortstop or Skip Schumaker? Your guess is as good as UZR's and DRS's, probably averaged together.