David Robertson added a new weapon to an already impressive Yankees bullpen

David Robertson has quietly carved himself a pretty significant role in Yankee history. He came up as the understudy of Mariano Rivera, didn’t allow a run in the 2009 playoffs, came “home” midway through last season to be the best reliever in a stacked bullpen for 2017’s ALCS run, and of course gave us some of the best gifs and photos in recent Yankee history:

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In 2018, Robertson’s been more of the same. His strikeouts are a little down, and his walk rate is a little up, but he’s posted a 2.77 ERA, and a 2.76 FIP shows that that’s not a mirage. He’s been one of the most dependable arms in a great bullpen, and hasn’t given up an earned run since July. As impressive as that all is, what’s most noteworthy about his season is that at the age of 33, he’s been able to change his pitch mix.

Everyone knows that Robertson throws a great cutter. Again, when you’re apprentice to Mariano freakin’ Rivera, you better throw a cut fastball. For years, David’s paired that cutter with a sharp curveball, one that he’s been able to throw in the strike zone when needed and in the dirt for a whiff. Since returning to the Yankees though, he’s brought out a new weapon:

David Robertson has added a slider! For the first time in his life, he’s really become a true three pitch pitcher. More than that, it’s a pretty good pitch. Since the end of July, he’s surrendered exactly one hit off his slider, with a 30.7% whiff rate. Aside from the newness of the pitch itself, it’s proved useful when you look at Robertson’s velocity:

The addition of a “middle” pitch in terms of speed is a hugely useful asset for a normally two-pitch pitcher. Facing Robertson in the past meant that a hitter could sit fastball, since a ten or so mile per hour difference between pitches is easy for a major league hitter to pick up. This is why Robertson has had to have such great command of his curveball for his career; if hitters are able to just sit on the pitch, you have to be able to throw it in the strike zone to keep them honest.

By adding a pitch in that 86 mph-ish zone, Robertson’s free to move around the plate a lot more with his other pitches. Instead of get-me-over curveballs keeping hitters honest, the loss of such wild disparity in pitch velocity keeps the hitters on their toes.

There’s one thing I still can’t figure out about the slider though, and it’s when Robertson actually throws it. Aside from watching the radar gun, there’s not much movement difference between the slider and curve - about 2” both horizontally and vertically. Even watching Saturday night’s dominant relief appearence against the Mariners, it was hard to tell whether any were thrown at all, even though Statcast tells us three were, two of them swung through.

This makes me think that Robertson has taken a page out of Dellin Betances’ book, throwing what’s essentially the same pitch and varying the pressure on delivery and velocity to distinguish a slider from a curveball. If that’s the case, it’s quite amusing that Robertson picked up one pitch from a great Yankee reliever at the beginning of his career, and learned a second from another great Yankee reliever at the age of 33.

One thing that pops up in my writing and thinking about baseball is the need to constantly improve. Every player and front office is desperately seeking an edge over the competition, and established veterans are at greater risk than ever of losing jobs to their young teammates. For Robertson to unveil a whole new pitch, and throw it well, shows that he’s hungry to keep getting better, and has his sights set on a multi-year contract as free agency approaches. If all three pitches stay this effective, it’s hard to argue that he wouldn’t be worth it.