Relievers are often called upon when a strikeout is necessary to prevent the other team from scoring. Here are the five relievers that are best at striking hitters out, based on their K/9 rate.
Heath Bell is the leader of the best bullpen in the majors—that of the San Diego Padres. As their closer, he has struck out opponents at a staggering 11.57 K/9. He throws a fastball that touches 94 miles per hour on the radar gun and a curveball with five-plus inches of break.
Brian Wilson's 96 miles-per-hour fastball paired with a hard slider (88 miles-per-hour, three inches of horizontal movement) have led him to post an impressive 12.47 K/9 rate this season.
Hanrahan has posted a 12.55 K/9 rate this season, thanks to a mid-90s fastball and a mid-80s slider with a three-inch break. He'll also occasionally throw a low-80s changeup, to throw hitters off-balance.
Wagner has been a dominant reliever for the past decade and a half, and he shows no signs of slowing down, despite going through surgery. He's put up a top-notch 12.82 K/9 rate this season, thanks to a high-90s fastball and a low-80s slider with nasty movement.
Carlos Marmol has had little control this season, averaging a BB/9 over five. He makes up for it, though, with his dominant strikeout totals. He is currently averaging 16.17 K/9, thanks to a nasty duo of pitches—a hard slider and a mid-90s fastball.
Luke Gregerson (Padres), Tyler Clippard (Nationals), Sean Marshall (Cubs), Francisco Rodriguez (Mets), and Frank Francisco (Rangers) all average a 10-plus K/9 rate.