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FORT MYERS, FLA. — Ask Twins catchers for their opinion on the nastiest pitch they've caught in camp, and closer Jhoan Duran is the easy answer.

That's fair. Duran does things nobody else in the world can do with a 104-mph fastball and an offspeed pitch, a splinker, that can somehow reach 100 mph.

The second-most popular response, by a wide margin, is Griffin Jax's slider.

"For how hard he throws it and how much movement it has, I've never seen anything like that," said catcher Patrick Winkel, one of the nonroster invitees to camp. "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."

It's a pitch Jax created by chance. During the canceled 2020 minor league season, he was one of the prospects invited to pitch at the team's alternate site in St. Paul. It was a monotonous setting with live batting practice sessions against teammates and simulated games without a full defense.

Facing the same hitters each time, there was no element of surprise. The teammates Jax faced all knew how his fastball, changeup and curveball moved. After about five weeks at the alternate site, toying with the ball, Jax deployed his slider for the first time.

"I saw it move straight to the left," Jax said. "The pitching coach at the time was like, 'What was that?' I said, 'I don't know. I was just messing around.' He goes, 'Well, do that again.' We just built it off that and messing with it the last couple of years got it to the place it is now."

Jax's slider, analytically, rates among the best in the majors in vertical movement, but it's much faster than others with a similar profile. The depth of the pitch generates a high groundball rate, and a lot of whiffs. He struck out 68 batters in 65⅓ innings last year, and 47 strikeouts came through the slider.

"You don't really see a whole lot of spin until it gets just about to the plate, then it takes a left turn," catcher Brian O'Keefe said. "It's one of those sliders that you see and you're like, that's a little different."

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Griffin Jax career statistics

Jax threw a slurve, a mix of a curveball and slider, when he pitched at Air Force, but it wasn't like the pitch he throws now. Before reporting to the alternate site in 2020, one of his friends he played catch with during the pandemic showed him a slider grip.

"He was with the Yankees organization, and they were teaching him this pitch," Jax said. "It turned out to be the sweeper, so that organization was a little bit ahead of the curve of throwing that pitch. He taught it to me, and we started playing catch with it."

Once Twins coaches encouraged Jax to throw his sweepy slider more often, he experimented with the pressure he placed on different fingers and the way the baseball's seams were oriented in his hand. When he debuted as a starting pitcher in 2021, his slider accounted for about a third of his pitches, according to Statcast.

"Like any new pitch, it takes a while, and it takes a lot of game reps to lock in," Jax said. "In '21, probably the reason I got called up was because I was throwing it in the minors, and I was doing really well with it."

Jax proved he could be a successful setup man last year, often handling the eighth inning in front of Duran. Jax was dominant in the postseason, striking out five of the 12 batters he faced while giving up one hit.

He hasn't changed the way he grips his slider over the past two seasons, but he is somehow finding ways to throw it harder. Jax's slider sat at 88-90 mph in a recent live batting practice session, which unsurprisingly featured a few swings and misses.

"As long as it keeps the movement, the harder it is, the better it is going to be," he said.