David Robertson’s Awesome, Strange Arsenal

You’re not going to get anywhere using dollars per projected wins when it comes to relievers. Not usually. You have to pay a premium if you’re buying an established closer with a multi-year track record — that’s what the past shows. And so if we look at David Robertson, and the four-year, $46 million deal he just received from the White Sox through that lens, we won’t find happiness.

But what happens when we investigate how this reliever with below-average velocity has managed to be so dominant for the last four years? Does the deal look better?

Relievers just get paid more than you might think they should within the framework of wins above replacement. Rafael Soriano got $14 million for his work last season. Jonathan Papelbon got $12.5 million. Craig Kimbrel, Jim Johnson, Joe Nathan, and Brian Wilson each got more than ten million dollars. Maybe two of those guys were worth that kind of money.

On the other hand, we just came off a postseason run where the dominance of the Royals’ bullpen was a daily topic. Greg Holland anchored that pen. Robertson has a lot in common with Holland, especially when you add one piece of home park information to the list:

If Greg Holland is one of the best three relievers in the game, then David Robertson is right there with him. To be more correct — if Greg Holland has been one of the best three relievers in the game, then David Robertson has been right there with him.

The question is always about what’s more likely going forward.

One thing we know about pitchers is that they continually lose velocity. But it’s worse for relievers — their velocity loss contributes to a more drastic reduction in strikeout rate than you see with starters. Over the course of the next four years, the soon-to-be 30-year-old Robertson is likely to lose as much as four miles per hour on his fastball and over six strikeouts per nine if he follows the standard aging of a reliever. If he’s throwing 88 and striking out fewer than seven batters per nine, he won’t be worth this contract.

But when it comes to David Robertson *specifically*, it seems that velocity is not hugely important to his success. You see that 92 mph fastball and wonder how he does it. One part of the equation is that he’s releasing the ball 14 inches closer to home plate than most pitchers. Maybe that, and good command, is how Robertson has managed to make it work with below-average velocity for a reliever.

Except look back on Robertson’s early career, and it’s not clear he’s always had great command. For the first four years of his career, he walked a guy every two innings. And then something happened. He started throwing the ball off the plate down more.

Still, that’s a lot of fastballs right down the middle there. Only 24 pitchers threw a higher percentage of their pitches in that part of the zone last year. Robertson threw nearly 4% of his pitches down the heart of the zone. Felix Hernandez threw 0.5% of his pitches in that same middle box.

It helps that Robertson’s fastball has unique movement. Called a cutter in some places, the pitch has the horizontal movement of a cutter (0.88, average for a righty is .67), but the ride of a rising fastball (10 inches, average is 6.1). That’s a weird pitch. It actually has a decent amount in common with an elite cutter in the game — Kenley Jansen’s (2.5 Pfx_x, 9.7 PFx_z). By results, though, the two cutters aren’t equals (7% whiff rate for Robertson, 17% for Jansen).

Of course, there’s also Robertson’s vaunted breaker. His knuckle curve had the third-best whiff rate on baseball last season among yakkers (minimum 200 thrown). With over eight inches of drop, it has almost twice the drop of the league average curveball.

It’s not all about velocity for Robertson, but he does things to make his velocity play up. His command looks better by walk rates than it does when you examine his heatmaps, but the movement on his fastball makes it hard to decipher even as it comes down broadstreet. And with a whopping 18 inches of difference between the vertical movement on his cutter and curveball, his pitches may complement each other very well.

It’s unclear if we’ve solved David Robertson, but maybe that’s the point. There’s enough that’s funky about him that hitters haven’t figured him out over the last 200 innings, so maybe we can say that’ll continue if his health holds up.