Stephen Strasburg has allegedly thrown 58 sliders this season. After four games that number seems neither noteworthy of indicative of anything. That is, unless you compare it to the last few seasons.

First – the number. In the last 56 starts he made prior to the beginning of 2016, he threw 18 sliders in total. This year, he’s averaging 14 a start. On Sunday, he threw 20. That’s a big difference.

So, did Strasburg learn a new pitch?

Well, it’s actually not first time he’s thrown a bunch of sliders at the beginning of the season. He started the first three games in 2014 with 40 sliders, before abandoning it almost completely. Prior to that, he hadn’t thrown any.

He’s now gone 4 starts into a season while still leaning heavily on his slider, which is a new thing. I’m not the first to notice this – Jeff Sullivan of Fangraphs and Mike Petriello of both pointed out the surprise appearance of the pitch few weeks ago.

However, despite the fact that PitchF/X calls it a slider, neither of those two are sure that it actually is one. To add to the mystery, Nats beat writer Jamal Collier asked him about it after his first start, and Strasburg denied even using a slider. So what’s going on?

Well, Sullivan and Petriello don’t really seem to care too much about what the pitch is, they are more concerned with the results, and I don’t blame them. After all, he could call it the Strazzer and as long he’s getting guys out, we’d be happy. They submit that it might be something more like a cutter, or somewhere in between a slider and a cutter, known as – I’m not making this up – a “slutter.”

It looks like a cutter in some ways, especially the results. Unlike his fastball and his changeup, which both have whiff rates in the double digits this season, the slider has the lowest whiff rate of all his pitches at just over 5%. His fastball whiff rate will likely come down, Strasburg had previously used mostly his offspeed stuff to get swings and misses. Over the years, it’s been the changeup and curve that made hitters look silly – the slider’s low rate may be an indicator that he’s not using it to get swings and misses.

Sullivan notes that he is throwing them at the knees, rather than burying them in the dirt, like typical sliders. Not only that, “It’s like he was looking for weak, sawed-off contact. That’s what a cutter is used for. So, I don’t know, maybe we should think of this as a cutter instead.” And he’s gotten a high groundball rate off of it, another sign that it might be used like a cutter.

Comparing it to ones he threw at the beginning of 2014, it certainly seems like a different pitch, something new. It comes in at almost 90 mph, his 2014 sliders were more like 87. It has slightly more horizontal movement, and significantly less vertical movement than the old sliders. So, maybe it is a hybrid. But if he’s not talking, how can we know?

Well, maybe there’s a clue to what he’s throwing, and that’s because while the slutter isn’t the most popular pitch in the world, there are a few guys who do throw it. Jake Arrieta is one, apparently, and he’s doing pretty well. But there’s another guy who seems to use it , and that guy is team leader, fan favorite and mentor-to-all… Jonathan Papelbon.

Papelbon has been throwing a slutter since he debuted, probably because he likes the name. While he uses it more like a slider, throwing it low and away, he insists it’s not a real slider. He called it a “cross between a slider and a cutter” because he tried, but couldn’t master the cutter.

Was this a result of some spring training interaction between the two? Perhaps Strasburg is denying using a slider because he isn’t using one. Maybe he learned from Papelbon to throw a hybrid, and is using it like a cut fastball even if it registers more like a slider. If it’s on the cutter-slider spectrum, perhaps it leans towards cutter.

Either way, it seems effective, and Strasburg seems to like using it so far this season. It’s worth watching to see if he continues to rely on this slutter (Strasburg’s Strutter, perhaps?), and if it remains effective once the league sees it a bit more.

By Charlie