The grandson of Johnny O'Brien, who played in parts of six Major League seasons in the '50s, Riley O'Brien spent two years at Everett (Wash.) CC before transferring to NAIA College of Idaho and becoming the school’s highest-drafted player in 2017, when the Rays took him in the eighth round. The athleticism, size and raw potential that had endeared O’Brien to Rays amateur scouts began to show in his first full season, with the right-hander garnering All-Star honors in the Midwest League before finishing the season at Class A Advanced Charlotte. The Stone Crabs’ Opening Day starter in 2019, he dominated out of the gate to earn an early May promotion to Double-A Montgomery and continued to pitch well in the Southern League before a bout of elbow soreness prompted the Rays to shut him down in July.
A plus athlete with a loose arm and projectable 6-foot-4 frame, O’Brien’s velocity has steadily improved as he’s added strength and gained experienced on the mound. After pitching with an upper-80s/low-90s fastball at the outset of his career, O'Brien comfortably sat 92-95 mph and bumped 97 during his breakout 2019 campaign. He's long shown feel for spinning the ball and can flash above-average to plus with both of his breaking balls. Most scouts like his slider, a swing-and-miss out-pitch with nasty bite, more than his curve, though the latter certainly has its moments. O’Brien also has feel for throwing a changeup that has average potential.
While his control and command are both below average right now, O’Brien’s athletic delivery and clean arm action should allow him to make the necessary gains. He could have a mid-rotation future if can refine his secondary pitches and learn to throw more strikes. If that doesn’t work out, O’Brien could be a late-inning force on the strength of his fastball-breaking ball combo.