The Red Sox have made one of the strangest moves of their deadline push, agreeing to send Marcelo Mayer to the San Francisco Giants for reliever Erik Miller, according to MLB insider Ken Rosenthal of The Athletic. Jeff Passan reported that the deal is still pending a medical evaluation.
For Boston, this is a stunner. Mayer was once the kind of prospect the organization would have been expected to protect at almost any cost, but Craig Breslow has clearly taken an aggressive approach this deadline. Since taking over as chief baseball officer, he has traded five of Boston’s six most recent first-round picks.
Miller gives the Red Sox the bullpen help they’ve been looking for. The 28-year-old left-hander from Stanford, drafted by the Philadelphia Phillies in the fourth round of the 2019 MLB Draft, has been a strong late-inning option for San Francisco this season. He owns a 2.76 ERA with 45 strikeouts and 22 walks across 32.2 innings, has piled up 12.4 strikeouts per nine innings, and righties are hitting just .183 against him.
That kind of arm matters for Boston right now. Interim manager Chad Tracy recently said Garrett Whitlock is "beat up," a reflection of how heavily he’s been used, and Jovani Morán and Greg Weissert have already thrown 45 and 43.2 innings, respectively. Miller should help ease that load and deepen the back end of the bullpen.
Mayer’s time in the majors never really caught fire the way the Red Sox hoped. Boston called him up for his debut after an injury to Alex Bregman last season, and the move came too early. Since then, Mayer has hit .223/.278/.346 in 114 games, and he has struggled badly against right-handed pitching, batting .215 with a .599 OPS.
The Red Sox are clearly banking on what remains of Mayer’s value after a disappointing 2026 showing. It’s a far cry from the kind of return Boston might have envisioned when Mayer was one of its top young talents, and much less than the sort of player fans once imagined could headline a deal. Miller, meanwhile, is under team control through the 2030 season and should slot in as a weapon ahead of Aroldis Chapman.
It’s a tough ending for Mayer in Boston, but prospects don’t always turn into what teams expect.
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