BREAKING: Red Sox Part Ways With Marcelo Mayer In Exchange for Giants Reliever Erik Miller

That 15-game winning streak officially broke something in Craig Breslow. He's done trying to build slowly and methodically around a core group of prospects. Instead, he's certain it's time to go all-in.

Following their blockbuster move for Adley Rutschman earlier in the day and a swap of Tyler Uberstine for Eli White, the Boston Red Sox have now traded former top prospect Marcelo Mayer to the San Francisco Giants, reuniting him with Rafael Devers. In exchange, they're getting reliever Erik Miller.

This is an aggressive move by the front office, and not just because Miller is a 28-year-old reliever with a 2.76 ERA. Mayer was one of the fabled "Big 3" Red Sox prospects alongside Kristian Campbell and Roman Anthony, both of whom signed long-term extensions with the franchise. The former, unfortunately, is struggling in Triple-A this year and comes with a lot of buyer's remorse, while the latter has looked elite while healthy but is currently dealing with a long-term hand injury.

Mayer is an excellent infield defender and was the supposed heir to Trevor Story's throne at shortstop. Unfortunately, he just didn't hit at the big-league level (.625 OPS, 69 wRC+) and, like Campbell, has regressed in 2026. He should earn a lot of playing time in San Francisco, where the rebuilding Giants can afford to let him figure things out in low-pressure games.

As for Miller, he fills the left-handed set-up man quota Breslow has been desperate to meet. His peripherals are outstanding, as he ranks in the 90th percentile or above in strikeout rate, whiff rate, expected batting average allowed, average exit velocity allowed, hard-hit rate, and groundball rate. In other words, he does almost everything well on the mound, which makes it easy to buy into his 2.76 ERA despite terrible command.

He's also under team control through 2029, meaning he could be the closer of the future once Aroldis Chapman finally decides to hang 'em up. Losing Mayer is a painful price to pay, but Miller is good enough to make that gamble pay off.

The Sox are also receiving Carlos Gutierrez in the deal, per MassLive's Christopher Smith. The 21-year-old outfielder has a 124 wRC+ in High-A this season.

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