It should come as no surprise that Cincinnati's Aroldis Chapman is the very best relief pitcher when it comes to striking pitchers out. He leads all relievers (with at least 30 innings pitched) in K%, striking out a ridiculous 51.5% of all batters he has faced. He also has the most K/9 of any relief pitcher, and it isn't really very close, at 17.54 batters per nine.

Consider that over a nine-inning game, Chapman would strike out a million hitters. Or, something like it.

His nERD of 1.27, however, is actually second among all bullpen arms to the man who is number four on this list. (You'll have to keep clicking in order to see who that is.) Chapman's ERA of 2.36, while very good, pales in comparison to his FIP of 0.95, meaning he's been hurt by a little bit of bad luck, which drags down his rWAR to 1.4, behind five other relief pitchers on this list. FanGraphs' WAR likes him a lot better, at 2.3, 5th among all MLB relief pitchers.

But there's no debate about it. Chapman is the most feared closer in the game, averaging 100.3 miles per hour on his fastball this season. According to MLB.com's Mark Sheldon, if Chapman can maintain that number, he will become the first pitcher to average more than 100 miles per hour on his fastball for an entire season since the Pitch F/x tracking system was instituted in 2006.