SF Giants have chance to revive fallen prospect after Erik Miller swap with Red Sox

Of the five trades Buster Posey and Zack Minasian made in the 24 hours leading up to today’s trade deadline, most were focused on stockpiling the farm system for future success. When the Giants traded Erik Miller and Carlos Gutierrez to the Red Sox, though, the motivation was a good balance of helping the present and future.

Marcelo Mayer, a top-10 prospect in all of baseball just three years ago, rapidly fell out of favor with the Red Sox after making his major league debut last year. In his 44 games in 2025, Mayer hit .228/.272/.404 (80 wRC+) with four home runs before missing six weeks to season-ending wrist surgery.

If his rookie season was disappointing for a prospect of Mayer’s pedigree, his sophomore season has been far worse. Though his walk rate has risen incrementally, his .220/.282/.312 line (63 wRC+) has made him virtually unplayable. His hard-hit percentage has fallen from 51.7% in 2025 to 35.8% this year, so even when he is able to make contact, it’s been poor.

He’s the second castoff the Giants have scooped up from the Red Sox, and both apparently were saddled with the baggage of being labelled disturbers of the clubhouse. While concrete details of how Mayer and Roman Anthony’s friendship were a distraction are few and far between, there were enough reports about it to where there may have been a little fire underneath all the smoke. The interim Red Sox manager, Chad Tracy, had to address the rumors himself to say there wasn’t any validity to them, but it was at least a little eyebrow-raising that he acknowledged the reports at all.

Taking all that into account, the Sox acquiring Curtis Mead from the Nationals on July 25th was the writing on the wall that they weren’t expecting Mayer to be a big part of their plans. Their giving up on Mayer, potentially, could work for the Giants’ benefit. Just listen to MLB.com’s analysis of him back in 2023 –

“The consensus among scouts was that Mayer was both the best hitter and best defender in his Draft class, a potential combination of Corey Seager's bat and Brandon Crawford's glove.”

The Giants bought low, but Marcelo Mayer could still have a high ceiling

That is some lofty, albeit probably unrealistic, praise. He certainly has a smooth left-handed swing and good instincts that help compensate for him being a bit oversized for the average middle infielder. He’s mostly played second base in the big leagues, and that’s where he figures to get most of his action with the Giants now that Luis Arraez packed his bags for Philly. Of course, like a lot of Giants players, he’ll have to come off the IL first – he went down back on June 25th to a stress reaction in his forearm, and his return is still TBD.

When he does come back, though, the rest of 2026 is the perfect opportunity to let him have an audition and see what he can do with a change of scenery. In addition to playing the keystone, he was drafted as a shortstop and also has experience at third base, which gives the Giants extra flexibility and could potentially come in handy if one of Matt Chapman or Willy Adames is jettisoned over the offseason. Mayer comes with plenty of years of control, as he’s not a free agent until after 2031.

For now, Mayer is coming into an environment where there will be a lot less pressure on him to succeed right away. A notoriously demanding fanbase, Red Sox supporters aren’t known for having endless patience for young prospects who are too overhyped to ever live up to expectations. Even with parts of two big league seasons under his belt, Mayer is still only 23 – plenty of players are still years away from The Call at that age.

San Francisco, though pretty much just playing out the year at this point, could be an ideal training ground for Mayer to prove himself. He should have a big chip on his shoulder – his stock has fallen precipitously, and if he fails at this opportunity too, there could be real questions of whether he has a future in the big leagues at all. So maybe there is some pressure on you, Marcelo – just don’t think about it.

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