Sometime last year, it became clear just how much David Robertson learned from his teammate Mariano Rivera. Though he still throws a plus curveball, Robertson's delivery and fastball has grown to mimic the future Hall of Famer's.
The two look similar on the mound, and PITCHf/x says their cutters are only a few inches in movement away from each other. With Rivera retiring this offseason, it's easy to start thinking of Robertson as the future closer, but just how similar is he to Rivera?
Rivera's cutter is outlined in blue above, and Robertson's cutter is outlined in red. PITCHf/x says that Rivera is getting about an inch and a half of additional movement into left-handed hitters compared to Robertson, and that's pretty clear from the GIF above. That's not to say Robertson's cutter is in any way bad, in fact Brooks Baseball has batters hitting just .225 with a .363 slugging against it. In comparison, Rivera is allowing a .235 batting average with just a .286 slugging. Robertson might become a highly successful closer one day, as he's already emerged as one of the best relievers in the game, but it's hard to imagine anyone else throwing the cutter like Mariano Rivera.