The Red Sox traded Robertson and Victor Santos (undisclosed) to the Cardinals on Friday in exchange for Tyler O'Neill (foot), Alex Speier of The Boston Globe reports.
Robertson had a tough time finding his footing in 2023, posting a 6.04 ERA and 1.75 WHIP across 22.1 innings between the Dodgers and Red Sox. St. Louis' relatively weak bullpen gives Robertson a better chance at sticking around in the majors to begin next season, but he likely won't be relied upon in many high-leverage situations.