The Cardinals and Mariners got together on a minor trade yesterday, with St. Louis acquiring right-hander Riley O’Brien from the Mariners, according to MLB.com’s transactions log. The return headed to Seattle in exchange for O’Brien is not currently known, but figures to be insignificant. O’Brien is slated to hit minor league free agency if not added to the 40-man roster. While the Cardinals have not announced that O’Brien’s contract will be selected, they have just 38 players on their 40-man meaning no corresponding move would be necessary to do so.
O’Brien, 28, was an eighth-round pick in the 2017 draft by Tampa Bay. He pitched well in three seasons with the organization while seeing time as both a starter and reliever. By the 2019 season, he had reached Double-A with a 3.93 ERA and 24.2% strikeout rate in 68 2/3 innings of work at the level. Though O’Brien did not pitch in the 2020 campaign thanks to the cancelled minor league season, he was swapped to the Reds in a deadline deal that brought Cody Reed to the Rays that summer.
O’Brien spent almost the entire 2021 season at the Reds’ Triple-A affiliate in Louisville, where he struggled somewhat to a 4.55 ERA across 23 appearances (22 starts). Despite that uninspiring performance, O’Brien was called up to make his big league debut near the end of September. Unfortunately, his sole appearance in the big leagues during the 2021 season did not go well as he walked three and allowed two home runs in just 1 1/3 innings of work. Cincinnati retained O’Brien on their 40-man roster throughout the 2021-22 offseason but ultimately designated the then-27-year-old righty for assignment in April in order to make room for left-hander Nick Lodolo on the 40-man roster.
That led the Reds to ship O’Brien to Seattle, where the Mariners had an open 40-man roster spot to offer the righty. While he returned to the big leagues in May and pitched a scoreless inning out of the bullpen, O’Brien’s 2022 season left plenty to be desired overall as he struggled to convert to full-time relief, posting a 7.03 ERA in 39 2/3 innings of work at the Triple-A level after being outrighted off the club’s 40-man roster in June.
Difficult as the 2022 season was, O’Brien returned to the Mariners in 2023 and pitched far better than he had the year before. Though he did not manager to make his way back onto the 40-man roster, O’Brien dominated the hitter-friendly PCL to the tune of a 2.29 ERA in 55 innings of work this year while striking out a whopping 37.7% of batters faced. Given those fantastic numbers at the Triple-A level this year, it’s easy to see why the Cardinals, who are known to be looking for bullpen upgrades this offseason, would be interested in taking a chance on O’Brien and finding out if his strong 2023 season in the minors could carry over to the big leagues in 2024.