Did the Warthen Slider Drag the Mets Down?

The Mets’ quick slide from a National League championship in 2015 to 90 losses this season had to claim a victim. Manager Terry Collins appears to be one of them: according to reports, he’s unlikely to return next year. Now, pitching coach Dan Warthen is a candidate to join him on the chopping block in New York.

It makes sense to some degree. The Mets’ fate over the past few years has been tied closely to the quality of the pitching staff. Once a clear strength of the club, that staff represented a weakness for this year’s team. But much of that weakness was a product of injury, and injuries hit every team at a seemingly random pace. Is Warthen a scapegoat here, or is he somehow directly responsible for the current situation?

Two years ago, Warthen’s brand of slider appeared to be a revelation. Somewhere between a cutter and true slider, the hard breaking ball seemed responsible for the breakouts of multiple pitchers: Jacob deGrom, Jeurys Familia, Matt Harvey, Steven Matz, Jenrry Mejia, Hansel Robles, and (of course) Noah Syndergaard.

The Mets consistently led the league in slider velocity and may have even inspired other teams to try out the harder version of the pitch.

While velocity is linked to slider whiffs, the relationship isn’t as strong as you’d think. And though the Mets have routinely produced the league’s hardest sliders, they may not have had the best ones.

There are a couple of ways to evaluate the effectiveness of a pitch. To begin, here’s a three-year look at slider whiff rates across the league, grouped by team:

As you can see, the Mets actually placed among the bottom third of all teams by this measure. That’s not definitively bad, but it’s not encouraging, either.

But whiffs aren’t the only measure of success for a single offering. What if we combine whiffs with ground balls, to account for the two best outcomes over which a pitcher has control? I’ve done that below, grading all sliders on a scale of 20-80, with 50 representing the major-league average. Since a small velocity differential between the slider and fastball was linked to ground-ball rate in the study linked here, maybe it’s not surprising the pitch does a little better here. Still, it’s not as dominant as it might seem when Noah Syndergaard is throwing it at 94 mph.

The pitch has confounded hitters to some extent, but maybe not as much as we thought it might. And this doesn’t even account for another possible effect of the pitch: injury. Look back at that list of pitchers at the top; it’s hard to find one who hasn’t spent significant time on the disabled list.

Of course, every pitcher seems to need a blow. An executive once told me off the record that the most surprising thing he learned from working in baseball is that “every pitcher is injured at all times. It’s just how much they can handle.” Especially now with the 10-day DL, it seems folly to draw any straight lines between a few pitcher injuries and a pitch they share in common. They also all threw hard, for example, and that’s been shown to be the biggest single stressor.

About that finding, though. Studies using a Motus sleeve to measure stress by pitch type reveal that fastballs tax the arm more than all other offerings. But fastballs are thrown harder than all those other offerings, too. Here’s what stress by pitch type looks like if you normalize for velocity, as Kyle Boddy at Driveline Baseball did:

Breaking balls emerge as the most stressful pitches per mph by this methodology. Now the alarm bells are going off. The Warthen Slider is the hardest slider in baseball by mph. You’re not throwing the curveball 90-plus mph, but there are plenty of Mets throwing sliders 90-plus mph. The Warthen Slider might be the most stressful pitch in baseball.

Of course, there are caveats, which Boddy is careful to note. We don’t know how the stress is distributed differently in each pitch type. We don’t know how this stress-per-mph relationship works within a pitcher. At Saber Seminar, for example, Glenn Fleisig from the American Sports Medicine Institute demonstrated that, yes, more velocity is generally more stressful, but it also matters how close to a pitcher’s personal max those fastballs are thrown. Syndergaard throwing his fastball at 96, when he can throw it at 100, is less stressful than deGrom throwing his fastball at 96. Perhaps sliders work the same way.

The uncertainty that remains in the relationship between pitch type and injury should hold us back from blaming Warthen for what occurred the last couple years under his watch. The coach himself brushed aside concerns when I asked him: “It’s easy on the arm when done correctly, it’s not one of those pitches that you try to make break,” he said.

What we can do is give him some credit for all the pitchers who broke out under his watch, especially since so many of them told Kristie Ackert at the New York Daily News they enjoy working with the coach, which echoes what David Laurila and I heard — without prompting — when we asked the pitchers themselves about their adjustments.

So take your pick. We’re still feeling around in the dark on injuries. Maybe Dan Warthen’s slider is risky. At the same time, we can see high-end production from so many of these pitchers pretty plainly — and they’re pointing directly to the coach. Maybe they should give him another year to rehabilitate all those arms he helped develop.