There are many ways to get a batter out, and while some pitchers rely on sheer stuff to blow away a batter, most other pitchers rely on a combination of their pitch movements, velocities, and location to methodically confuse hitters. A pitcher like Mariano Rivera didn't rely on a repertoire of disorienting pitches, he simply threw a cutter with incredible late horizontal break over and over again. Meanwhile, when a pitcher like Andy Pettitte lost velocity, he learned to throw with different movements and speeds to play up some of his declining pitches. Today, Masahiro Tanaka uses both styles, throwing a high-rising four-seamer, a hard breaking sinker, and a brutal splitter that make each subsequent pitch look like they're moving even more than they really are.
Unlike Rivera, and much more like David Robertson, Dellin Betances uses more than one pitch. When a reliever, the right-hander used to throw a sinker and a changeup, but as a reliever he's stuck with his two strongest pitches in his four-seamer and slurve. His two-pitch repertoire may be more complicated than Rivera's, but both of his pitches rely on a tremendous amount of movement and velocity. There is no need for him to set hitters up, and as we've seen in the past, Betances can throw slurve after slurve and still earn swings and misses with virtually no command. So what makes his two pitches so special?
His four-seam fastball is obviously fast, and in 2014 he's averaging 96.78 mph on it according to Brooks Baseball. A few years ago, this velocity alone would be good enough to put him in the realm of top relievers, but in today's game this velocity isn't as rare. According to Baseball Prospectus' leader board, Betances ranks 34th in reliever velocity on his four-seamer. Betances' secret to success in the bullpen was also the defining factor of his failure as a starter. When the right-hander throws his four-seamer, he doesn't know where it's going.
This scatter chart above shows the pitch movement of everything he's thrown in the 2014 season. The red and yellow fastballs have automatically been broken into four-seamers and cutters by PITCHf/x algorithm, however they're all the same four-seamer. Some of his fastballs break up and into right-handed batters, while others obtain cutter movement that has equal break into left-handed batters. The range of different movement he's able to obtain with his four-seamer is incredible, but also contributes to the lack of control that took him out of the rotation last year.
His breaking ball is also an important part of his bullpen success. Like the four-seamer, the range of movement on this pitch can vary greatly. There's so much movement and so much velocity, that it's hard to identify what to call it. While Brooks Baseball calls it a curveball, the pitch averages nearly 84 mph, which makes it much more like a slider. Betances calls the pitch a slurve.
In terms of velocity and movement, the pitch sits in the mid-80's with around seven inches of break into left-handed hitters and falls over four inches below the no-spin axis. It's hard to find another pitcher with the same movement and velocity, as those with so much movement only hit the upper-70's, and those in the mid-80's rarely have much more vertical drop below the no-spin axis. In 2014, Drew Storen of the Nationals has the most comparable slider, while Yoervis Medina of the Mariners has the most comparable curveball.
Between his four-seamer and slurve, Betances has two plus pitches that show tremendous movement and velocity. He has the ability to throw these pitches past anyone, but his erratic movement also confuses batters. There's little need for Betances to set batters up, since none of his four-seamers or slurves are alike. What was a problem for him as a starter has become his ultimate weapon, no one can predict how these pitches move, including himself.