Article: Should Hayden Wesneski Trade in His Sweeper for a Gyro Slider?

[Matthew Trueblood]

As the Cubs ponder ways to make external upgrades to the pitching staff, let's look at one important young pitcher already on the team who might have another level of performance within reach.

Image courtesy of © Lon Horwedel-USA TODAY Sports

Last week at Baseball Prospectus, the excellent Mario Delgado Genzor wrote an insightful piece about the art and science of pitching. Specifically, he broke down something he calls the Pronator's Triangle, and discussed how pitchers' wired-in physical movement preferences might inform the construction and effectiveness of their arsenals. It's a really good article. If you're a BP subscriber, make sure to check it out.

As I read Mario's work, I thought instantly about Hayden Wesneski. Even in a season that saw Keegan Thompson's career go completely off the rails, no pitcher on the Cubs roster was more disappointing than Wesneski in 2023. He had looked like a potential mid-rotation starter in his brief audition in 2022, but that didn't translate to success in a full-fledged opportunity to join the rotation when the team broke camp last spring. Instead, he quickly had to be demoted back to Triple-A Iowa. He spent the rest of the season yo-yoing between the minors and the majors, often working as a long reliever or swingman, and only found even a semblance of a groove after moving into short relief in September.

Going into the season, we knew there would be challenges ahead. As I wrote last spring, Wesneski had a significant hurdle to clear when he joined the organization. He had a deep pitch mix, but he also had a bifurcated release point. In other words, he released some of his pitches from one arm slot, and others from another. That kind of split makes it easier for hitters to eliminate certain offerings as possibilities right out of the hand, and it can have implications for both durability and command, to boot. 

Wesneski tried to reconcile his arm slots, but it didn't stick. He still throws his four-seamer and cutter from one angle, and his sinker, sweeping slider, and changeup from another.

That's a problem--one that helps explain why lefties hit .298/.369/.617 against him in 2023. It essentially disqualifies him as a starter in the big leagues, and limits his utility even out of the bullpen. With a problem that can be so large-scale and multi-systemic, though, that leaves a huge, scary question: What's the solution? You almost have to choose between rebuilding his entire delivery and rebuilding his entire pitch mix, and if you do the former, you might end up having to do the latter, anyway.

Enter Delgado Genzor, with his delightfully clear communication of a nuanced pitching subject. The Pronator's Triangle describes the relationship between the plot points when you chart a pitcher's horizontal and vertical movement against one another, if they belong to the class of pitchers who tend to pronate through release of the ball. ('Pronation,' for the uninitiated, is what your high-school pitching coach probably called, 'turning it over.' It's not always a true turn of the arm or hand to tilt the palm toward a same-handed batter's box, but it is, at least, staying through the inside of the ball at release.)

When we talk about pronation, we're most often talking about sinkers and changeups, but some guys do have perfectly useful four-seamers despite a tendency toward pronation. As Delgado Genzor also wrote, guys with a preference for pronation (as opposed to supination, which is the motion around the outside of the ball we usually associate with cutters, sliders, and curveballs) can still have very effective breaking balls. These are almost always 'gyro' sliders, in the modern parlance. They don't have a lot of sweep; they turn like a cement truck and drop mostly due to gravity. 

Here's an example of a Pronator's Triangle, cribbed straight from the article. It's the movement profiles by pitch category for Luis Castillo, who was at the center of the piece overall. 

Notice that, technically speaking, Castillo's breaking stuff doesn't have much spin-induced movement. It only 'moves' due to gravity, as the gyro spin slows down its progress toward the plate and doesn't produce the same resistance to that force as backspin of any form would.

Compare that chart to Wesneski's movement plot (by pitch type, not category, because I think we'll gain more clarity this way in his case.)

It's pretty simple. Wesneski's sweeper stretches the Pronator's Triangle beyond its breaking point. That sweeper works best off his four-seamer, in terms of movement, but his four-seamer comes from a different slot, so the deception is gone. His changeup also works better off the four-seamer than off the sinker, because he doesn't generate enough run on the change to differentiate it from that sinker. Again, though, that would only be true if movement were the only relevant variable. Instead, we have to account for the fact that the four-seamer comes from a different release point than the change, too. 

That leaves us with a couple of divergent paths ahead for Wesneski. One option is to focus on the four-seamer and the cutter, and try to learn a splitter to go with it. That would be a three-pitch mix good enough to work against both righties and lefties, if he could command it sufficiently and stay healthy along the way. The alternative would be sticking with the sinker and the changeup, leaning more into pronation from that slot to engender better movement on the change, and trading in the sweeper for a gyro slider. 

Wesneski had such a pitch early in 2023. He utilized one earlier in his pro career, too, but the Yankees prefer to give pitchers like him a sweeper as they near the majors. When he was throwing the gyro slider in the spring, though, Wesneski released it from that four-seamer and cutter slot, not the slot from which he throws his pronator stuff.

If either of these avenues promised surefire success, the Cubs and Wesneski already would have plunged down it at full speed. Instead, all the data tells us there are boulders in either path for the righthander. He might not be able to find three pitches he can command (and which have the right kind of movement profile to neutralize hitters) from either slot. He might never find the thing that unlocks what seems like significant upside. After watching a lot of Wesneski for the last year, though, I would feel much more confident trying the second path. 

That means scrapping the sweeper, and re-training Wesneski to throw the gyro slider from a lower slot. It means changing the way he attacks the strike zone, and probably where he sets up on the mound. It means making the four-seamer a tertiary weapon and some hard work in finding feel for a circle change. That's a lot of possible pitfalls, and it's not to mention the biggest lift involved: getting Wesneski to buy in on leaving behind the pitch that made him low-grade famous, and which has netted him the best grades since before he even debuted in MLB--that sweeper. 

For those reasons, the team might go the other way. Learning a splitter and raising the slot on the sweeper is probably easier than doing what I just listed. Either road is worth exploring. Motor preference theory (pronation vs. supination) is not a perfect or complete one. Still, laying it out this way helps us see that continuing to try everything Wesneski tried throughout 2023 is a non-starter. One way or another, he needs to make big, big changes. This is just a paradigm to help us see which ones are possible.

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[We Got The Whole 9]

He should work on a splitter

[Bertz]

This is really good!  At a high level, the issues Wesnesk had really seem similar to what Alzolay had in 2021.  Alzolay  became a little more north/south instead of east/west snd bumped up his 4-seamer/Cutter/Changeup usage at the expense of his sinker/slider.  I imagine similar gradual changes would work with Wesneski, but that release point split you point out could be the fly in the ointment.  I looked at Alzolay and he had one two, but just like an inch or two not ~6 inches like Wesneski.

[Tryptamine]

If he can be even average against lefties, he's good enough against righties to be a solid starter. He's just so incredibly bad against lefties. 

[Matthew Trueblood]

15 hours ago, We Got The Whole 9 said:

He should work on a splitter

I love the splitter in general, so I'd lean this way, too. But I'm not sure it's a good fit for Wesneski's mode of movement--or at least, that the arsenal he'd be leaning into by choosing that tweak over a change of slider shape is the one that best suits him. It'll be interesting to see which way they go. 

[Matthew Trueblood]

14 hours ago, Tryptamine said:

If he can be even average against lefties, he's good enough against righties to be a solid starter. He's just so incredibly bad against lefties.