This under-the-radar Cardinals pitcher is flashing lethal stuff in camp

Riley O'Brien is opening eyes in the St. Louis Cardinals winter camp with his disgusting sweeper, and he could become a weapon out of the bullpen.

Tampa Bay Rays v Seattle Mariners
Tampa Bay Rays v Seattle Mariners / Steph Chambers/GettyImages

The St. Louis Cardinals may have excavated a gem after plucking right-handed pitcher Riley O'Brien from the Seattle Mariners for cash in November. The 29-year-old O'Brien has only 2.1 career major league innings under his belt, but he could be poised to achieve big things in 2024 after flashing some dazzling pitches in the Cardinals' winter workouts.

According to's John Denton, O'Brien's sweeper had a jaw-dropping 21 inches of horizontal break in his latest appearance. The average sweeper, according to, has around 15 inches of horizontal movement. At 84 mph, it's a hard curveball, which makes its huge break even more deadly.

O'Brien also has a sinker that produced an exceptional 66.7% ground ball rate in 2023, along with slider that he began implementing last year, which he learned at Driveline. This arsenal allowed O'Brien to plow through Triple-A hitters in 2023, as he accumulated 86 strikeouts in only 55 innings en route to a Pacific Coast League All-Star nod. The one weakness he still displays is in his control, but even that improved from 6.8 walks allowed per nine innings to 5.1.

The Mariners have been a pitcher development factory over the past few seasons, and with the Cardinals now a part of the sweeper revolution as they attempt to return to relevance in the National League, poaching a pitcher with elite movement like O'Brien was a shrewd move.

The Cardinals don't appear to have a ton of competition for roster spots to open the season, with the bullpen likely comprising Ryan Helsley, Giovanny Gallegos, Keynan Middleton, JoJo Romero, Andrew Kittredge, John King and Ryan Fernandez if the team chooses to utilize a six-man rotation. But with injuries virtually guaranteed to strike, the Cardinals will be in need of reinforcements on the farm. As of now, that's where O'Brien should come in.

If O'Brien excels in Spring Training, the Cardinals may have to reconsider their planned bullpen configuration. His curveball would rank among the best in the major leagues in terms of its break, and with his sinker and slider serving as strong complements to the pitch, O'Brien could be a late bloomer who finds sustained success wearing the birds on the bat.