Unlike offensive metrics, there isn't one truly reliable way to measure the defensive efficiency of MLB players.
But the league is getting close.
While OPS is heralded as maybe the best tool to evaluate hitters, tracking other stats like homers, OBP and AVG are still useful in their own right.
Defensively, you can't simply go by the fewest number of errors. Aramis Ramirez might have fewer errors at third base than David Wright, but if Wright gets to nearly twice as many batted balls, you can't really compare the two, can you?
At the MIT Sloan Sports Analytics this weekend, MLB Advanced Media announced a new, nameless system that tracks the speed and efficiency of fielders based on a variety of different factors, including batted ball speed and how fast defenders react. Deadspin has more information and an example of the system at work, tracking a fly ball caught by Atlanta's Jason Heyward to end a game last year.
This system was put through a trial run last year at Citi Field in New York and will spend another season at the Mets' home ballpark in 2014, as well as Target Field in Minnesota and Wrigley Field North (aka Miller Park) in Milwaukee.
There is a lot still unknown about the new system, but it's a revolutionary tool to help effectively gauge the value of defenders across the league.
Now, if only the system could measure TWTW, then we'd really be getting somewhere.