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The knuckleball is returning to Major League Baseball. The San Diego Padres are calling up knuckleballer Matt Waldron to start Saturday's home game against the Washington Nationals, according to MLB.com. It marks Waldron's MLB debut and will make him the first knuckleballer to pitch in the big leagues since Mickey Jannis appeared in one game for the Baltimore Orioles in 2021.

Waldron, 26, was a traditional pitcher with a low-90s fastball, a slider, and a changeup when Cleveland selected him in the 18th round of the 2019 draft. They traded him to the Padres as part of the Mike Clevinger deal in 2020, and Waldron began the conversion into a knuckleballer in spring training 2021. Here's Sports Illustrated with the story:

He'd started playing around with the pitch as a kid, growing up in Nebraska, and had always been fond of it. But he'd never thought seriously about trying it in a game. At spring training in 2021, however, Waldron threw a few knuckleballs while joking around with some fellow pitchers. A team staffer took notice and made a request: Do that in front of the Rapsodo. The pitch-tracking device confirmed the desirably low spin rate, and so the team encouraged him to work on it, maybe even try it out in games. That year in High A, he began throwing it as a secondary pitch, just a few per game. Midway through the season, he got a message from the front office: What if he threw the knuckleball more often? Like, say, 80% of the time, starting the next week?

"I kind of immediately was like, Okay, sounds good," Waldron laughs. "I didn't really realize how big of a commitment it was. But fortunately it's worked out."  

Baseball America ranked Waldron the No. 30 prospect in San Diego's system last year and said he throws two versions of his knuckleball: "a low-80s one and a low-70s version." Former Cy Young winner R.A. Dickey threw two distinct versions of a knuckleball during his career as well. Here is Waldron's knuckleball in action:

This season, Waldron owns a 7.02 ERA in 66 2/3 Triple-A innings with the high strikeout (10.1 per nine innings) and home run (1.5 per nine innings) rates you typically see with a knuckleballer. That said, the Padres' Triple-A affiliate plays in El Paso, one of the most hitter friendly environments in the minors. El Paso as a team has an .869 OPS and 6.58 ERA.

The Padres have not yet announced a roster move for Waldron, or the plan with the rest of their rotation. Michael Wacha, arguably San Diego's best starter this season (2.90 ERA in 80 2/3 innings) was originally lined up to start Saturday, but manager Bob Melvin announced Friday he would skip the start due to shoulder fatigue. The Padres will take a 36-39 record in Friday's series opener with the Nationals.

Waldron is the only known knuckleballer in affiliated professional baseball. Jannis currently pitches for the High Point Rockers of the independent Atlantic League.