The problem with defensive metrics is, there's no single figure that is universally agreed upon as reliable. With pitching, you can look at ERA+ to get a good feel for a pitcher's performance; some may prefer the likes of FIP, but the two are generally going to be pretty close to each other. Same with OPS+ and wRC+ - if a batter does well in one, they will probably be looked upon kindly by the other. But when it comes to an objective measure of defense, there is much less consensus. As we'll see, stats can supposedly be looking at the same plays by the same players, and come up with radically different outcomes.
Measuring the 2015 Diamondbacks defense: An introduction
