My favorite metric when it comes to slotting relief pitchers is win probability added (WPA). According to FanGraphs.com, the top five relievers in that category last season were: Oakland's Blake Treinen, Milwaukee's Jeremy Jeffress, Seattle's Edwin Diaz, Boston's Craig Kimbrel and Milwaukee's Josh Hader. If you followed last season closely, you don't even have to go to the numbers to realize that's a solid listing of the best relievers in baseball.
MLB tiers: Ranking baseball's best relievers
