Why Red Sox Finally Dumped Marcelo Mayer in Trade for Giants Lefty

Erik Miller could be quite good in Boston...

Jun 9, 2026; St. Petersburg, Florida, USA; Boston Red Sox shortstop Marcelo Mayer (11) fields a ground ball in the sixth inning against the Tampa Bay Rays at Tropicana Field. Mandatory Credit: Jonathan Dyer-Imagn Images | IMAGN IMAGES via Reuters Connect

As the Boston Red Sox traded away a new wave of prospects in the Adley Rutschman deal on Monday, they also said goodbye to one of the headliners of the last wave.

Shortstop Marcelo Mayer, the Red Sox's 2021 first-round pick and former No. 1 overall prospect, was reportedly dealt to the San Francisco Giants on Monday just before the 6 p.m. ET trade deadline. Ken Rosenthal of The Athletic was first to report the deal was close.

In exchange, the Red Sox got hard-throwing lefty Erik Miller, according to multiple reports. The shortstop of the future is gone with just 114 major league games under his belt, but the Red Sox got an arm they believe can bolster their playoff odds.

What made Red Sox pull plug?

Jun 19, 2026; Seattle, Washington, USA; Boston Red Sox infielder Marcelo Mayer (11) hits an RBI double in the sixth inning against the Seattle Mariners at T-Mobile Park. Mandatory Credit: Kevin Ng-Imagn Images | IMAGN IMAGES via Reuters Connect

Mayer will turn 24 in December, so he's still quite young in major league terms. But the Red Sox had to be getting wary of all his injury issues; in fact, if you listened to whispers coming from somewhere vague within the organization throughout the year, it was pretty clear that the Red Sox weren't thrilled with the youngster's progress.

Since his full-season debut in 2022, Mayer has never appeared in 100 games in a season. He made it through three months healthy this season, but turned out to be playing through a hairline fracture in his left forearm. His return is still in question, and the Red Sox were searching for more concrete answers.

In Miller, they hope they have something solid. The 28-year-old lefty, who comes with 3 1/2 years of control, regularly touches 100 mph with his heavy fastball. In 38 games this season, he sports a 2.76 ERA with 45 punchouts in 32 2/3 innings. He's got 22 walks, so control is an issue, but the .198 opposing batting average speaks volumes.

With top prospect Franklin Arias reaching Triple-A, the Red Sox just weren't willing to wait around any longer for Mayer to figure things out. They got something for him while they could, and what could have been a great story about a homegrown position player has become a cautionary tale about the injury bug.