This story was excerpted from Alex Stumpf’s Pirates Beat newsletter. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

PITTSBURGH -- Colin Holderman doesn’t know who taught him his best pitch.

Holderman knows when and where it happened. But who taught him? That’s a tough one.

It was 2022, and Holderman was at Triple-A Syracuse in the Mets’ organization, ready to take on the Yankees’ affiliate in Scranton, Pa. Jake Reed, one of his teammates, called him over to talk to a friend of a friend who was in New York's organization. The friend noticed Holderman threw a slider, and he suggested instead throwing a new pitch the Yanks were teaching their pitchers called the “whirly.”

Holderman tried it out that night, and his bullpen catcher immediately started hyping it up. That was enough for Holderman to try it out in a game, and he very quickly learned he had a new breaking ball.

“He changed my career. I wish I knew the guy’s name,” Holderman said during the Pirates’ most recent road trip in Toronto.

That whirly -- or sweeper, as it is more commonly referred to now across the Major Leagues and in pitch classifications -- has become Holderman’s go-to offering this season, and one of the most valuable pitches on the Pirates’ staff. Entering Wednesday, opponents are hitting just .114 against it, and 18 of Holderman's 26 strikeouts have come on the pitch. Going by Baseball Savant’s run value, it has been worth 5 runs above average, making it the top offering of any pitch in the Bucs’ bullpen this season.

And in a year where the Pirates’ bullpen has been mostly inconsistent, Holderman has been the most reliable arm out of the group, posting a 0.93 ERA in 20 appearances.

Holderman didn’t shy away from trying out the pitch in the Minors in 2022, but it wasn’t until 2023 that it got a proper introduction in the Majors. Originally, he primarily used it as an offspeed pitch, playing off of the movement of his cutter while also changing velocities from his sinker, which normally sits in the high 90s.

• Pirates' pitchers learning to embrace the cutter

Holderman relied on the sinker plenty in his first full Major League season in 2023, throwing it 50.1% of the time, compared to 29.6% for his sweeper and 20.3% for his cutter. That’s a pretty standard pitch mix, especially for a reliever who can hit triple digits. This year, it’s a different story. Holderman is throwing his sweeper 48.9% of the time and his sinker 32.5%. He’s become a power pitcher who isn’t maxing out on velocity that often, and it’s working.

“I’m saving that for a little bit later,” Holderman said. “We’re trying to build up easy, especially with the way I started.”

That’s a reference to an illness Holderman caught during Spring Training that caused him to lose almost 20 pounds and start the season on the 15-day injured list. He’s back to 100% now, and his velocity has returned to form, but the sweeper is still his primary pitch. It’s what Holderman wanted to do last year, but it put pressure on his right wrist and limited him. This year, he changed the grip so he’s not clamping down on it as hard, which has let him throw it more often and more consistently.

“It’s a weapon,” manager Derek Shelton said. “It’s the weapon now, and I think the fact that he’s been able to have really good feel for it. Last year, it was more strike to ball all the time, and now it’s more strike to strike than strike to ball. Sometimes it’s ball to ball, and he’s still getting swings. I think we’re just seeing the evolution of him being able to have feel for the pitch.”

Holderman attributes a lot of the sweeper's success to how it plays off the cutter. It moves and spins similarly, just slower. Plus, both pitches come out of the hand at a very similar spot.

“If they’re coming out of the hand at the same spot, it’s really hard to recognize,” said pitching coach Oscar Marin. “And hitters have to respect that he still throws 100. That’s not easy. It’s not like I can sit on this or sit on the other. When that sweeper’s 85 [mph], and then [the fastball’s] 98? I think that’s what makes it effective.”

It’s safe to say whomever that stranger was two years ago gave Holderman some solid advice.

“He gave me some good information and changed my life,” Holderman said. “My other slider was pretty good, so you’ll never know. But the whirly has been big for me.”