Aidan Keenan, the younger brother of former Mariners draft pick Tyler Keenan, is lighting up radar guns with a fastball reportedly topping out at 99 MPH, making him one of the most talked-about pitching prospects for the 2026 MLB Draft. This right-handed hurler, who grew up playing baseball in Morgan Hills, California, is turning heads with his raw stuff, even as he navigates a challenging college career at Stanford.
From High School Star to College Hurler
Keenan was an absolute force in high school. He snagged the 2021 Blossom Valley Athletic League Sophomore of the Year and the 2023 Blossom Valley Athletic League Pitcher of the Year awards, among others. His senior season was insane: a 0.74 ERA over 47.0 innings with 75 strikeouts. He was one of California's top prep players for the 2023 draft, but with a rock-solid commitment to Stanford, he withdrew from the class. College has been a different beast, though. His freshman year in 2024 saw him appear in just 5 games, starting 2, with a 6.75 ERA over 6.2 innings, allowing 5 earned runs, 4 hits, 10 walks, and 7 strikeouts. Rough start, right?The Stuff Is Still Electric, Despite Injury
Coach Esquer switched Keenan to an exclusive bullpen role for his sophomore 2025 season, and things looked a bit better. He appeared in 24 games, posting a 5.59 ERA in 37.0 innings, with 33 hits allowed, 14 walks, and 43 strikeouts. That summer, he looked solid in a pair of starts for the Santa Barbara Foresters in the California Collegiate League. This 2026 season, as a junior, he was moved into the Cardinals' starting rotation, but an oblique injury in mid-March sidelined him for most of it. Still, in his 7 starts (five pre-injury in February and March, two post-injury in May), he posted a 5.82 ERA in 21.2 innings, with 22 hits allowed, 21 walks, and 25 strikeouts. The 6'2", 200-pound righty throws from a low-three-quarters arm slot with a high-tempo delivery. His fastball, which can hit 99 MPH and sits in the mid-90s, has crazy riding life. The command needs work, but the potential is there. He complements it with a mid-80s, high-spin slider that has tight vertical drop and impressive horizontal movement, a high-80s cutter that gets weak contact, and two variants of a changeup. This is the kind of arm that makes you wonder about the future, especially with that Mariners connection through his brother. While Aidan keeps honing his craft, our Mariners just put on a clinic, beating the Tampa Bay Rays 8-2. We're talking early season form, folks, and seeing our boys crush it like that while prospects with family ties to the Emerald City are flashing 99 MPH makes you pretty pumped for what's ahead!This article was created with AI assistance and reviewed by Seattle On Tap editorial staff. Always verify information with official team sources.