Giants to Trade Erik Miller to Red Sox for Prized Infielder Marcelo Mayer

The San Francisco Giants were not done making moves just minutes before Monday’s MLB trade deadline.

San Francisco Giants relief pitcher Erik Miller. | IMAGN IMAGES via Reuters Connect

The San Francisco Giants used every minute they could on Monday to make trades to try and improve the franchise for the future.

With less than an hour to go before the 6 p.m. eastern deadline, the Giants were reportedly trading reliever Erik Miller to the Boston Red Sox for second baseman Marcelo Mayer, a former top prospect in that organization who has struggled with his bat in 114 Major League games.

The Athletic's Ken Rosenthal was among the reporters on the trade.

The Red Sox clearly valued Miller's arm as they are bolstering their bullpen for a potential playoff run after one of the hottest Julys in Major League history.

San Francisco, meanwhile, needed a second baseman after they traded Luis Arraez to the Philadelphia Phillies earlier on Monday. That trade also included reliever Caleb Kilian.

Erik Miller Traded

Boston Red Sox shortstop Marcelo Mayer. | IMAGN IMAGES via Reuters Connect

Miller has been a solid left-handed reliever for the Giants for the past three seasons and leaves the organization with an overall record of 10-6 and a 3.05 ERA.

This season he's been rock solid, as he has a 2-0 record and a 2.76 ERA in 38 games, along with 10 holds and four saves in five chances. Had he not been traded, he likely would have been the pitcher to replace Kilian as the closer.

The Red Sox selected Mayer with the No. 4 overall pick in the 2021 MLB draft, and he signed for a 6.6 million signing bonus. At one time he was considered one of the best prospects in the Red Sox organization and in all of baseball and made his Major League debut in 2025. But his bat has never quite picked up the way it did in the minor leagues.

He joins the Giants with a career slash of .223/.278/.346 with seven home runs and 32 RBI.

San Francisco has been wheeling and dealing in the final 24 hours of the trade deadline. The Giants shipped starting pitcher Tyler Mahle to the Atlanta Braves for reliever Anthony Molina, who was optioned to Triple-A Sacramento.

As part of the Arraez-Kilian trade, San Francisco received prospects in return, including RHP Ramon Marquez and RHP Marty Gair. The Giants also traded left-handed starting pitcher Robbie Ray and received two more prospects in RHP Miguel Mendez and IF Joniel Hernandez.

San Francisco also traded outfielder Heliot Ramos to the New York Yankees but the return on the deal wasn’t immediately available because it was still being finalized.