Knuckleball vs. Knuckleball: First Such Pitching Duel in Over 25 Years

Matt Waldron, on a rehab assignment for the San Diego Padres, and Gabe Mosser of the Seattle Mariners' organization made history at Cheney Stadium in Tacoma on Thursday, staging professional baseball's first confirmed knuckleball-vs.-knuckleball pitching duel in over 25 years. The Tacoma Rainiers defeated the El Paso Chihuahuas 3-1 in a game that turned as much on the physics of spin, or the deliberate absence of it, as it did on the score.

The last time two knuckleball starters shared a mound on opposite sides was September 15, 2000, when Tim Wakefield of the Boston Red Sox and Steve Sparks of the Detroit Tigers matched up. Since Statcast began logging data in 2008, just 10 players have thrown a knuckleball at the Major League level, and only 13 have done so at Triple-A since 2023, which is why Cheney Stadium felt like an accidental time capsule on Thursday.

Waldron, who used the knuckleball on 74 percent of his pitches in the big leagues in 2024, arrived with a modified approach. He dialed knuckleball usage down to 26.2 percent of offerings but still generated four whiffs on 10 swings, and he threw the pitch more than 2 mph harder than his prior MLB velocity. The result: six strikeouts over four scoreless innings.

Mosser's line was arguably more impressive given the workload. The right-hander, who signed a Minor League free-agent deal with the Mariners in January 2026 after time in the Phillies' organization, held El Paso to one run across six full innings. Pitch-tracking systems officially credited him with just two knuckleballs during the game, one producing a groundout and one a foul ball, but Mosser said he threw it more often than was recorded. The knuckleball's unusual movement profile routinely causes tracking systems to misclassify it as a sweeper, changeup, or splitter. In 65 tracked Triple-A knuckleballs, Mosser has not allowed a single extra-base hit on balls put in play.

The two pitchers throw what amounts to the same pitch in name only. Waldron's is a traditional flutter knuckleball. Mosser described the distinction: "His is like a true knuckleball. I hold mine like a true knuckleball, but it kind of has more top spin than his, [mine] doesn't really shake as much. It's more of the low-spin tumble. It's a little bit different of a pitch, but still the same idea behind it." Waldron's fluttering, unpredictable movement drives swing-and-miss; Mosser's tumbling variant generates groundball contact, which explains why he logged six innings despite the pitch-tracking undercount on his primary offering.

The game also served as a reunion. Waldron and Mosser are former Padres system teammates, having played together at High-A Fort Wayne in 2021, Double-A San Antonio in 2022, and Triple-A El Paso in 2024. They shared the Peoria Sports Complex again this spring training. Thursday was the first time they ever faced each other as opponents.

Waldron, who made his MLB debut June 24, 2023 at Petco Park and became the first pitcher to throw a knuckleball in a major league game since Mickey Jannis of the Baltimore Orioles did so in June 2021, is working back from injury. Adding more than 2 mph to his knuckleball velocity while cutting its usage rate signals a deliberate evolution toward a mixed-arsenal approach that complicates advance scouting. Mosser, in his first season in the Mariners' system, delivered a six-inning, one-run performance against the only pitcher in recent MLB history to carry the knuckleball as a primary offering. Whether that earns him a big-league look in 2026 is now Seattle's call.