Royals have their own Mason Miller turning heads on the mound in Quad Cities

It can be tricky to track down details on Mason Miller—the baseball player. No, not the pitcher with the microscopic ERA since joining his new team earlier this season. And no, not the flamethrowing reliever who landed with the Padres at the trade deadline. This Mason Miller is the Kansas City Royals’ own: a 23-year-old southpaw carving up hitters with High-A Quad Cities.

Kansas City’s pitching pipeline has been filling up box scores and prospect chatter all season, but turning arms like Mason Miller into MLB contributors will be the true test of its viability. Drafted in the 13th round of the 2023 MLB Draft at 409th overall, the Florida Gulf Coast product struggled in his first taste of pro ball last year, posting a 7.76 ERA and 6.60 FIP across 14 appearances.

He wasn’t on many radars entering 2025, but something clicked over the offseason—now Miller is emerging as a name to watch as the season winds down.

Royals' Mason Miller is thriving in High-A Quad Cities this season

Miller earned a promotion from Low-A Columbia to Quad Cities and made his High-A debut on July 10. Since then, it’s been all systems go for the lefty.

He opened with seven straight scoreless outings, not allowing his first earned run until Aug. 20—over a month later. In nine appearances (eight of which have been starts) with the River Bandits, Miller has posted a stingy 0.57 ERA and 3.08 FIP across 31.1 innings.

He’s striking out hitters at an impressive 27.4% clip, though his 10.5% walk rate shows there’s still room for refinement. Even so, the box score doesn’t lie—that’s elite production from a freshly promoted arm.

The River Bandits are now using Miller as a traditional starter, a shift from the tweener and bulk roles he filled earlier this season with the Fireflies.

His longest outing came in his most recent start on Aug. 26, when he worked five innings, allowing just one hit and one earned run while matching a season high with six strikeouts. Miller carried the bulk of a dominant effort, as Quad Cities’ staff held the opposition to just two hits and one run on the night.

Miller isn’t a flamethrower like his namesakes, nor the type of pitcher who’ll wow scouts with raw stuff. Instead, he thrives on command and a flat fastball he locates well at the top of the zone. His breaking pitches can be erratic, but he lands more strikes than misses, and he’s unafraid to pitch to contact rather than nibble around the edges.

The lefty’s delivery is smooth and repeatable, with a steady routine on every pitch. His breaking ball—whether you call it a slider or a curve—has been his best weapon, baffling hitters and generating more whiffs than his changeup ever has.

Miller may not project to the same caliber as his Padres namesake in the closer’s role, but he’s doing the right things—and doing them well.