Sweeping Success: Can Captain Jax Take Command in Twins Bullpen?

Griffin Jax is having a ridiculous spring for the Twins. That's evident when you take a glance at this overall stats – zero runs allowed on three hits with 12 strikeouts and no walks in 7 ⅔ innings – but even more so when you dive into the underlying metrics. 

It's been noticed by his teammates, his opponents, and pitch data analysts who pay attention to specific traits. Jax isn't just pitching well and getting outs; he is blowing people away. Heading into his age-29 season, the right-hander appears to be unlocking the true peak of his powers – and at an ideal time for the Twins.

Minnesota's bullpen was shaping up as a major strength heading into the season, projected by FanGraphs as the second-best unit in the majors. That was before the team received a double-whammy of bad news last week: Caleb Thielbar's balky hamstring was not improving, and worse yet, Jhoan Durán had developed a moderate oblique strain. Both will open the season on the injured list, and given the nature of these soft-tissue injuries, the Twins should probably grow accustomed to life without them for awhile.

It's expected that two relievers will primarily be leaned upon to fill this high-leverage void in the late innings. Jax and Brock Stewart were already lined to play critical setup roles, but now will factor in at the very end of games, and in the very most pivotal of moments, which usually would've gone to Durán. Stewart is capable but needs to be handled very carefully given his injury history, meaning Jax figures to elevate as Rocco Baldelli's top bullpen ace.

Relative to Stewart, Jax can be ridden to some extent in the absence of Durán, counted on to throw multiple innings or pitch on consecutive days. Jax has been a durable and dependable workhorse out of the bullpen after originally coming up as a starter. With that in mind, it's hard to overstate just how impactful his presence can be early in the season.

Jax owes much of his success to an evolving hard slider (or "sweeper") that is among the filthiest pitches in all of baseball. Last year in his breakdown of best pitches in MLB, Eno Sarris of The Athletic gave Jax the silver medal for sweepers (behind only Sonny Gray): "It’s a true frisbee, with nearly 14 inches of horizontal movement. What’s remarkable about this pitch is that Jax gets above-average movement, but he also throws it nearly 87 mph on average."

Jax threw his sweeper 53% of the time last year, and it held opponents to a .197 average with a .243 xwOBA. Somehow, his best pitch seems to be getting better. As Bobby Nightengale of the Star Tribune reported earlier in camp, a few Twins catchers rated it this spring as the best pitch on the staff (lofty praise given Jax's peers).

"For how hard he throws it and how much movement it has, I've never seen anything like that," non-roster catcher Patrick Winkel told Nightengale. "Usually when you see a slider, if it's really hard, it doesn't move as much. It's shorter. He throws it 90 mph and it has the movement of one that is 82 — so much movement that it's incredible."

Data analyst Thomas Nestico, who breaks down in-depth pitch analytics for his Patreon TJ Stats, marveled recently about how Jax's sweeper has broken his tjStuff+ model this spring, producing absurd chase and whiff rates. I reached out to Thomas for his thoughts on Jax and what makes the pitch such a weapon, and he elaborated on Winkel's insight. 

"Griffin Jax's sweeper is one of the more unique pitches in baseball," he told me. "Its combination of glove-side movement and velocity is uncommon for pitchers. Generally, sliders which are thrown at higher velocities sacrifice movement, and the same the other way around. Jax defies this conventional thought by throwing one of the hardest sliders in the league, and with enough horizontal movement to classify it as a sweeper. This spring he increased the velocity on the sweeper to 88 mph, up from 86.7 mph from last season, while maintaining horizontal movement."

Baldelli, who turned to Jax a team-leading 71 times in the 2023 season, obviously appreciates the featured sweeper offering. But Rocco also values the reliever for his versatility, and the depth of his arsenal as a former starter. "Griffin is a rare reliever that has five legitimate major-league pitches," he told reporters in Fort Myers on Saturday. 

This spring, Jax has been working to reintroduce a curveball into his pitch mix. As Baldelli shared, "I think he and our pitching coaches are going to identify guys where that curveball should factor in ... We’re gonna have a plan for it."

"He can spin a baseball really effectively," the manager added, "and he can do it in a lot of different ways, and most people can’t do it in that many ways."

Last year, Jax was good – much better than his 3.86 ERA, which was inflated by a few spells of poor batted-ball outcomes. He was especially good late in the year when it counted most, posting a 2.45 ERA in September and carrying that success into October where he was flat-out dominant. Jax retired 11 of the 12 batters he faced in the playoffs, including five on strikeouts.

Yet somehow, Jax still seems to be finding another gear. Driven by his curiosity as a notorious "tinkerer" and the discipline developed through a military background (Jax is a Captain in the Air Force), he keeps on improving. It's an extremely exciting prospect at a time where the Twins need him to take control as the bullpen looks to reconfigure itself mid-flight in the early weeks. 

"I don’t really see a situation where I wouldn’t wanna pitch Griff," Baldelli said on Saturday. "You wish you could pitch him and use him every game, in some way, shape or form ... He has weapons to face any type of hitter that he might run up against."