Breaking down the key pitches in Zac Thornton's arsenal

An underwhelming Mets rotation benefitted from a surprising youth movement last season, and not just because Nolan McLean looked like an ace and Christian Scott impressed upon returning from Tommy John surgery.

Rookie left-hander Zac Thornton emerged as a rotation mainstay, even though he did not even receive an invitation to big league camp in Spring Training. The 24-year-old pitched to a 3.42 ERA across 15 starts after debuting as the club’s 13th-ranked prospect in mid-May.

Thornton is not your modern power pitcher who blows away hitters with high-octane heat. His average fastball velocity of 92.3 mph ranked in the 18th percentile of MLB. Thornton recorded just 63 strikeouts in 84 1/3 innings with a swing-and-miss rate (17.8%) that ranked eighth lowest among 178 pitchers to throw at least 80 innings last season.

How does a pitcher like that succeed in today’s game -- and as a rookie, no less?

“Just giving them different looks every time,” Thornton told MLB.com in August. “Those guys are the best hitters in the world, so I’ve got to keep them off balance.”

A diverse seven-pitch arsenal helps Thornton do just that. Let’s take a closer look at a few of Thornton’s critical offerings -- one pitch that he relies on the most, one that he wants to improve, and one that took a big step forward.

Cutter (32%, 89 mph)

It sure feels like everyone throws a cutter these days. Last season, 192 different pitchers threw at least 100 cutters, up from 140 pitchers just five years ago, in 2021. Pitchers are throwing multiple fastball shapes to make life difficult on hitters, and a cutter is the perfect compliment, a hard-ish offering designed to run in on a batter’s hands and induce weak contact.

But few pitchers use a cutter as their primary weapon. Thornton does. He threw his cutter 32% of the time last season, the fourth-highest usage rate by a starting pitcher.

Highest cutter usage, SP, 2026
Min. 1,000 pitches thrown

1. Ryan Johnson (LAA): 39.0%
2. Aaron Civale (CHC): 35.5%
3. Foster Griffin (CLE): 32.5%
4. Zac Thornton (NYM): 31.7%
5. Drew Rasmussen (TB): 28.9%

Whereas most pitchers will lean heavily on their four-seam fastball or sinker, Thornton turns to his cutter with confidence against both right-handed hitters (32%) and left-handed bats (31%). It’s something he’s done since college, and the Mets have leaned into what makes him unique.

“Our pitching and development guys have let me run with the cutter,” Thornton said. “I’ve always had the pitchability with it, so they’ve allowed me the freedom to throw it in the zone and out of the zone. They’ve told me to throw it. They say it’s a great pitch, it works well, and it gets hitters off balance.”

Slider (8%, 84.7 mph)

Look at the movement plot of Thornton’s pitches, and you’ll notice that there’s a good deal of overlap between his cutter and his slider.

So, what’s the difference? Why are they two different pitches?

Velocity is one reason. His cutter is an average of four ticks harder than his slider. And since the sliders are slower, they tend to drop more -- Thornton told us that anything with close to zero inches of Induced Vertical Break is a slider.

“The intentions are different, too,” Thornton said. “The sliders are going to be low on the plate, below the zone. The cutters are going to be up.”

We can see this pretty clearly on the heatmaps below.

Sweeper (16%, 80 mph)

Thornton releases the baseball with an over-the-top arm angle (50°), and most of his pitches have outlier vertical movement because of that high slot.

The sweeper is an exception. It breaks 12.8 inches to Thornton’s glove side, which isn’t eye-popping, but it is something different in the context of Thorton’s arsenal. Similarly, at 80 mph, it’s significantly slower than the other five pitches that Thornton throws at least 5% of the time.

That’s the point here: The sweeper gives hitters an entirely different look.

“It’s served me really well this year,” Thornton said. “It’s been a great tool to lefties, just to kind of get them off the 85-92 [mph] range. It’s given me a little bit of leeway.”

Opponents hit .200 with a 24.7% swing-and-miss rate against Thornton’s sweeper last season. Those were Thornton’s best numbers on any individual pitch in 2026.

Changeup (5%, 84 mph)

Of his seven individual pitches, this is the one that Thornton hopes to improve the most heading into 2027.

“Everyone’s told me my whole life that a good left-handed pitcher always has a changeup,” Thornton said. “I’ve always worked on it. It’s not like it sucks metrically, but I haven’t had as many reps with it as I’ve had with the cutter and everything.”

Thornton’s arm slot dictates the sort of movement profile that he gets on his changeup. It does not drop a ton or fade with plus arm-side movement; on its own, it's not a very inspiring pitch.

But so much of a changeup’s success is predicated on its relationship with a four-seam or two-seam fastball. Outlier changeups can work; just ask Dylan Cease, who finally honed a “riding” changeup that baffled hitters because he threw it with the same arm speed as his four-seamer, despite a large velo differential. Some other comparable left-handers, like Patrick Sandoval and Noah Cameron, excel with changeups that have unique movement profiles.

Thornton just has to build that relationship between his changeup and his fastball. In a small sample size -- Thornton threw just 58 changeups last season -- batters went 6-for-17 with a 10.3% swing-and-miss rate against the pitch.