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40 in 40: Trent Thornton’s spot on this roster makes no damn sense

Compels me though

Trent Thornton #46 of the Seattle Mariners pitches during the game between the Los Angeles Angels and the Seattle Mariners at T-Mobile Park on Monday, September 11, 2023
I do love a rec specs guy
Photo by Alika Jenner/MLB Photos via Getty Images

This is too many words about Trent Thornton. I’m sorry. It spun out of control because I find his spot on the roster confusing. True enough, he doesn’t have to be great as the fifth or sixth man on the bullpen depth chart. But in an offseason where the Mariners are pinching pennies like it’s 1840s Ireland, Jerry Dipoto’s choice to tender him a contract feels discordant. This is an organization whose biggest strength has been building a great bullpen on the cheap, so why are they spending $1.2 million on a guy with a career pitcher slash line of 4.53/4.67/4.44 (ERA/FIP/SIERA)?

He gets a reasonable number of called strikes, but without striking a lot of guys out. His walk rate was very good last year, but that was the first time he’d meaningfully beaten league average. He does manage contact pretty well. Except when he doesn’t: He was among the top 10% last year in expected wOBA on contact, but also gave up 1.44 home runs per nine innings. This is the profile of the guy on whom the Mariners are willing to spend a whole 1% of the payroll? It’s a mystery worthy of Knives Out’s Benoit Blanc.

A fifth-round pick out of UNC, the Astros grabbed Thornton in the same cursed 2015 Draft whose three first-round picks gave them Alex Bregman, Kyle Tucker and Mike Cameron’s son Daz, who they eventually flipped for Justin Verlander. (In Jack Z’s parting gift to us, the Mariners selected Andrew Moore and Braden Bishop, and although they are both perfect boys, neither of them was anywhere near as good at baseball as Bregman, Tucker, or Verlander. The most accomplished player the Mariners got that year was Tony Sandwiches. Hate the 2015 Draft! But I digress.)

After middling results as a minor-league starter, the Astros flipped Thornton to Toronto, where he had a decent rookie year in 2019. But loose bodies in his elbow and a less impressive 130-pitch 2020 put him on the ropes. So after the Blue Jays traded for Jose Berrios and promoted Alek Manoah in 2021, Thornton got squeezed out of the rotation and was converted to a reliever. More injuries and ineffectiveness eventually led to his designation for assignment in July 2023. The Mariners jumped the waivers line by trading Mason McCoy to the Jays to ensure they’d be the ones to get Thornton.

Along the way, he’s evolved a lot as a pitcher. When he came up, he had this beautiful high leg kick that made him one of the more fun pitchers to watch in a game where mechanics differentiation is slowly being stamped out by the tyrants ruling travel ball.

Actually, maybe his leg kick isn’t even in the top five fun things in that clip. But you get it. Tragically for the baseball aesthetes, he smoothed that out by 2021.

But more impactful than the mechanical changes, I think, has been the drastic alteration of his pitch mix over the years.

I’m hoping that evolution isn’t done yet. Because herein is my best guess as to what the Mariners are thinking. In particular, I want to focus on the slider family and the fastball family.

Let’s talk about the sliders first, which he’s been futzing with for years. In 2019, it was his most effective pitch. Then it was a very bad pitch in 2020, and he reshaped the pitch after that. But that was probably a mistake. He only threw 130 total pitches in 2020, just 31 of which were sliders. Maybe it was also getting beat up at the alternate site, I don’t know, but the 31-pitch MLB sample doesn’t seem like a good reason to reshape a pitch that had worked so well in his rookie year. The changes he made for 2021 included throwing it about five mph faster and cutting about 15 inches of its vertical break. It wasn’t a good tradeoff (-2.2 RV/100 (in a bad way)). And you can see in the chart above that he stopped throwing it so much, shelving it entirely in 2022.

But with the Mariners last year, he added another 3 mph without sacrificing any additional movement. Mid-80s with middling movement didn’t work. But high-80s with middling movement did, improving to a .180 wOBA against the pitch. We’ll come back to this.

When he shelved the proper slider in 2022, it was in favor of a new toy: a sweeper that’s pretty nasty. Thanks to elite spin, it’s turned out to be a great pitch for him, getting the best outcomes—called strikes or whiffs (CSW)—on it 37.7% of the time. That’s fifth out of the 86 pitchers who threw at least 100 sweepers last year. On top of that, when hitters made contact, the contact was bad, with an expected wOBA on contact of just .258 (with only the very occasional homer). Again, that’s fifth out of 86. He’s the only player in the top 10 by both CSW% and xwOBAcon. It kind of rules?

As for the fastball family, his most common pitch over his career has been his four-seamer, though it’s not that good now, nor has it ever been. Given its high spin, it’s a surprisingly lifeless offering. It’s average by CSW%, but that’s mostly propped up by called strikes while hitters wait out one they like, which they crush. His xwOBAcon on the pitch over the past two years is about .100 points worse than average, which is a lot. The combination of called strikes and damage on contact isn’t one that works without more swing and miss.

Meanwhile, he’s experimented with a sinker his whole career, and he finally started to rely on it a little bit after being traded to Seattle, throwing it a career-high 11.8% of the time. It doesn’t induce a lot of whiffs, but he’s got great command of it, throwing it in the shadow zone around the edges of the strike zone almost half the time. And when he misses, it almost never ends up in the heart of the plate. You could hang this heat map in the Frye:

Hitters just don’t get the barrel to a pitch like that, leading to a lot of weak contact like this:

Now look, I’m more of a pitch nurse practitioner compared to the pitch doctors on our staff in John, Kate, and Jake Mailhot. But it seems to me that if he has a fastball that’s good and a fastball that’s bad, he should throw the one that’s good more and the one that’s bad less. Is this the answer to the mystery of Trent Thornton’s roster spot?

Besides being a better pitch than the four-seamer, the sinker also makes for a better pair with his best pitch, the sweeper. Sinker-sweeper can work. You like that heat map of his sinker? Now look at it next to the one for his sweeper:

They spin in opposite directions, move in opposite directions, and land on different sides of the zone. His four-seamer is bad, it’s always been bad, and he’s always used it heavily. Maybe just stop? The sinker looks to be a much more solid foundation.

Now a complication here is that as good as the sweeper’s been, he should probably throw it less to lefties. You’re not really supposed to throw sweepers to opposite-handed hitters because they get a cleaner look at the horizontal break. But since developing the pitch, he’s thrown it to southpaws 20% of the time. And although that’s racked up called strikes at an elite rate, when lefties have swung, they’ve connected, and, predictably, they’ve crushed it. Of the four homers that have been hit off of it, two have been hit by lefties. (One of the other two was Giancarlo Stanton, which, you know, fair enough. The fourth was Martín Maldonado because Thornton’s a Seattle Mariner.) Lefties’ .403 wOBA on contact against Thornton’s sweeper is serious damage, and that’s somehow better than the xwOBA of .559, which is frankly not suitable for children. It’s Aaron Judge contact.

Relying on just the sinker to lefties isn’t a good plan either though because only Mariano Rivera can use just one pitch. And that’s why we put a pin in the improved hard slider. It could make a great second pitch to lefties. And hey, maybe keep the occasional sweeper to try to steal a strike; all those called strikes suggest there’s something to what he’s doing. But I think throwing it a lot less often would make it even harder to pick up when he does, while limiting the opportunities for damage. It’s something to consider.

On the other hand, maybe the way he gets all the called strikes is by keeping hitters off balance with the key being how many different pitches he throws. It’s tough to make prescriptions based on samples this small.

At bottom though, throwing his best pitches more often is so crazy it just might work. As vaunted as the Mariners pitching development team is, they don’t really spin straw into gold. To hear the players tell it, the pitching brain trust aren’t a bunch of wizards; they just advise the pitchers to do what they do best more often. To be sure, that’s probably an oversimplification—the best teachers have a way of making their students feel smart. But there is wisdom in focusing on positive reinforcement. For Trent Thornton, I’d think that would mean focusing on the sinker and sweeper. He was only in the organization for two months last year, and it seemed like maybe this was the direction they were headed with him.

Tendering Thornton a contract made no sense to me. I actually volunteered for his 40 in 40 as a joke. No one wanted this one, so I said I’d do it as payment for getting the sought-after Gilbert. But the danger in writing these 40 in 40s is that you try to solve the mystery, and in doing so, you can talk yourself into believing. Well, god help me, I think I’m starting to believe in Trent Thornton. Maybe there’s a $1.2 million pitcher in there after all.