The Oakland Athletics have opened the door to a new chapter in their pitching staff, and all eyes are on Mason Barnett as he steps onto the big-league stage. In a whirlwind of roster moves and injury woes, the Athletics have called up the hard-throwing right-hander from Triple-A Las Vegas, giving the former Kansas City Royals prospect his long-awaited shot in The Show. The timing? Couldn’t be more dramatic, with the club’s rotation battered by injuries and the season’s final month looming large.
It all started on August 26, 2025, when the Athletics officially placed left-handed pitcher Jacob Lopez on the 15-day injured list, retroactive to August 25, with a Grade 1 flexor strain in his left forearm. Lopez, who had been a revelation since arriving from Tampa Bay in the offseason—posting a sparkling 2.17 ERA since June 8, the third-lowest mark in Major League Baseball over that span—was forced out of his Sunday outing against the Mariners after experiencing forearm tightness. Manager Mark Kotsay didn’t mince words about the setback: “For Jacob, it’s unfortunate, with as well as he’s been throwing the baseball. But I think it’s the best of the news that we could be getting him back. We’re going to shut him down and give him some time. But there’s also maybe a chance to get him back at the end of the season, even if it’s an inning out of the bullpen.”
Lopez’s numbers before the injury were nothing short of impressive. He was tied for second among MLB rookies in strikeouts (111), tied for fourth in wins (seven), and ranked fourth in ERA (3.28) among all rookies with at least 81 innings pitched. The Athletics are holding out hope for his return before season’s end, but with just a handful of weeks remaining, it’s a race against the clock.
The injury bug didn’t stop there. On August 27, the club announced that right-handed pitcher Joey Estes would also hit the 15-day injured list, this time with a herniated disc in his lower back. Estes, who lacks a timetable for return, may not see the mound again this year. That’s two key arms down in as many days—a tough pill to swallow for a team already out of playoff contention, but one that opens the door for young talent to make their mark.
Enter Mason Barnett. The 24-year-old Georgia native was acquired from the Royals at the 2024 trade deadline, part of a package that sent reliever Lucas Erceg to Kansas City and also brought Will Klein and outfielder Jared Dickey to Oakland. At the time, the deal raised eyebrows—Kansas City had sent off a prized prospect, and the Athletics were betting big on Barnett’s future. Now, with the rotation in flux, it’s time to see what he can do on the sport’s brightest stage.
Barnett’s 2025 campaign with Triple-A Las Vegas has been something of a mixed bag. He leads the Pacific Coast League in games started (23) and has logged 119 innings over 25 total appearances—a testament to his durability. Manager Mark Kotsay was quick to point out, “For Mason, it’s a big day for him. It’s exciting. … He’s made every start this year. That says something about the durability.”
But the stat line tells a story of both promise and growing pains. Barnett posted a 6.13 ERA in those 119 innings, with a 6-2 record. The high ERA can be partially attributed to the hitter-friendly environment of the Pacific Coast League, where his home run-to-fly ball rate soared to 15.6%, the highest of his career. His strikeout rate—a solid 22.8%, or 9.38 per nine innings—demonstrates his ability to miss bats, but an 11.9% walk rate (4.92 per nine innings) highlights ongoing command issues.
Despite the uneven results, prospect evaluators remain bullish on Barnett’s upside. Baseball America ranks him as the ninth-best prospect in the Athletics’ system, while MLB Pipeline lists him just outside the top 10 at No. 11. Both outlets cite his four-pitch mix—anchored by a mid-90s four-seam fastball, plus a sweeper, curveball, and changeup—as evidence of mid-rotation potential. “He’s got a four-pitch mix,” Kotsay explained. “He’s a power-type arm that has the ability in short spurts to maximize the velocity. I’m excited for the opportunity to get to see him pitch in the big leagues for us.”
Originally drafted by Kansas City in the third round of the 2022 MLB Draft, Barnett was a fast riser through the Royals’ system. When the Royals traded him at the peak of his perceived value, many questioned whether the price for Erceg was too steep. In retrospect, with Erceg now a mainstay in the Kansas City bullpen and Barnett’s Triple-A struggles, the deal seems to have worked out for the Royals—at least for now.
For Barnett, the call-up comes at a crucial crossroads. With the Athletics out of playoff contention, the organization has the luxury to experiment with their young arms. Kotsay hinted at a flexible plan for Barnett, similar to the paths taken by fellow rookies Jack Perkins, J.T. Ginn, and Luis Morales, who began their big-league careers as multi-inning relievers before transitioning to the rotation. Whether Barnett sticks as a starter or carves out a role in bulk relief will depend on his performance over the coming weeks.
“The numbers aren’t great, but he was pitching in the [Pacific Coast League], which doesn’t tend to lead to pitchers doing great,” Kotsay admitted. “But a big fastball. We’ve got him here, and we’re going to assess where we think we can make adjustments with him.” The Athletics’ coaching staff will be watching closely, hoping that a change of scenery—and perhaps a bit less altitude—will help Barnett find the consistency that has eluded him in Triple-A.
Injuries have forced the Athletics’ hand, but they’ve also created an opportunity for a new wave of talent to step forward. With Lopez and Estes sidelined, the team’s focus shifts to player development and evaluation, setting the stage for what could be a pivotal offseason. For Barnett, every pitch is an audition—not just for a spot on next year’s roster, but for a lasting place in Oakland’s future plans.
As the season winds down and the Athletics navigate a turbulent stretch, Mason Barnett’s journey from prospect to big leaguer is just beginning. The coming weeks will offer a glimpse into his potential and the direction of Oakland’s pitching staff. One thing’s for sure—the spotlight is on, and Barnett will have every chance to prove he belongs.
