Defense doesn't matter in Fantasy leagues. Sure, there are some leagues that count errors, but they are fairly rare. For the most part, an owner doesn't care about owning a terrible defensive player as long as they produce at the plate. Though that's the case, there's still a way for defensive metrics to be useful in Fantasy leagues.
Stats: UZR (Ultimate Zone Rating) or DRS (Defensive Runs Saved)
Where can I find them: FanGraphs carries UZR. Baseball-Reference carries DRS.
What do they do: Both stats measure a player's defense in a way that doesn't utilize errors. Both systems use historical data to determine whether a fielder should make a play.
I still don't understand: These are really hard to explain in a short space. I wrote up a lengthy explanation of both here, though.
How can I use it: You won't use defensive metrics all that often for Fantasy. But it can pay off when teams make midseason trades or offseason signings. If a team picks up an elite infield defender, that bodes well for the ground ball pitchers on the staff. The opposite is true if they sign a third baseman who is a statue.
Example: This no longer works, but there was more hope for Rick Porcello this season based on the fact that Miguel Cabrera would move back to first and Jose Iglesias would take over third. There still is a thoughtDoug Fister will benefit from playing with a superior infield defense in Washington, though Ian Desmond has struggled early. We knew all of this in the offseason, and that's when you'll likely utilize defensive metrics for Fantasy.
What are the problems with this stat: Defensive metrics literally take seasons before they are reliable. A good sample for fielding stats is about three years. If you're going to look at these figures, you should also try and get a sense of what scouts are saying about these players. We don't have three years of data on Andrelton Simmons , but he's always been talked about as an elite defender. It's easier to buy his exceptional UZR when you supplement it with scouting information.
Anything else: We've covered quite a bit over the past few weeks, and defense seems to be a good stopping point. You won't use it much, but it can occasionally help you pick out sleepers. Defense has become a big part of the game in recent years, and real-life organizations are trying to use similar metrics to their advantage. Fantasy owners might as well try to find a leg up as well.
Next post: This may actually complete the "advanced stats for Fantasy" posts. I'll write up a little retrospective in the next few days.