The Boston Red Sox are sending young infielder Marcelo Mayer to the San Francisco Giants in exchange for left-handed reliever Erik Miller, the Athletic reports. 

The departure of Mayer out of Boston is a stunning one. The 23-year-old former No. 4 overall pick was not long ago one of the top prospects in baseball. Mayer, though, has thus failed to compete against pitching at the highest level. In 364 MLB plate appearances spread across this season and last, Mayer has a slash line of .223/.278/.346 with 24 walks against 84 strikeouts. Presently, he’s on the injured list because of a stress reaction in his forearm. Mayer has been on the IL since late June. He goes to the Giants as a high-upside change-of-scenery candidate with just more than a full year of major-league service time. 

Miller, 28 and a former Stanford product, has thrived across a limited sample since converting to a bullpen role. Over the last two seasons, he’s put up an ERA of 2.15 with 67 strikeouts and 36 unintentional walks in 62 ⅔ innings. He averages 97 mph with his sinker and fastball, and he has above a 50% whiff rate on his slider. Miller is under team control through the 2029 season.  

For the Red Sox, it’s another buyer’s move as they’ve barged back into contention and playoff position thanks to a 23-4 record since July 1. They entered deadline day coming off a road sweep of the two-time defending-champion Dodgers. Earlier on Monday, the Red Sox acquired catcher Adley Rutschman from the division rival Orioles. 

Here are our grades for this 1-for-1 swap.

Boston Red Sox: B

Already planning for postseason lefties

Miller is one of the game’s most unsung relievers and he’ll be especially useful in this version of the American League. The Red Sox could run into the Astros (Yordan Alvarez, Daulton Varsho), Yankees (Ben Rice, Cody Bellinger, Jazz Chisholm Jr.), or White Sox (Munetaka Murakami, Colson Montgomery) and their potent lefty bats in the postseason. As an added bonus, Miller will remain under team control through 2029.

San Francisco Giants: A

Can the Giants fix him?

Mayer is a big name more than anything right now. He’s had injury issues for years and hasn’t hit in the big leagues when healthy. That said, the Giants are one of the worst teams in baseball and flipping a reliever to buy low on a young player who not too long ago was one of the best prospects in the game is a savvy move. It may not work out, but it’s worth the dice roll. There’s a much better chance Mayer is part of the next contending Giants team than Miller.