Red Sox know exactly how to make an elite reliever out of already-dominant Erik Miller

Craig Breslow rewarded the Boston Red Sox on trade deadline day with major upgrades in key areas. The one that stole all the headlines was the addition of three-time All-Star Adley Rutschman, but in the final hour, he snagged a key bullpen piece.

The Sox added left-handed reliever Erik Miller from the San Francisco Giants. The 28-year-old has a 2.76 ERA in 32 ⅔ innings this season, with a 3.34 FIP, while owning a 12.4 K/9. Miller has also been consistently a late-inning reliever for San Fran, with 33 of his 38 appearances coming in the seventh inning or later. Miller also has three years of team control after 2026, which is likely why he cost a valuable piece like Marcelo Mayer.

A quick look at the former fourth-round pick's Baseball Savant page shows that he isn't just getting lucky either. Miller ranks in the 90th percentile or higher in xBA, Average Exit Velocity, Whiff%, K%, Hard-Hit%, and Groundball%. He throws a 97 MPH sinker with above-average movement and pairs that with an 86 MPH power slider. He throws those two about 85% of the time. 

Erik Miller's weakness is one the Red Sox know how to fix

Miller comes with one major weakness: he walks a lot of people. The lefty has a 6.1 BB/9 this season, and a 15.5 BB%, which is in the 1st percentile. He only lands his sinker in the zone just over 50% of the time, and his slider is only 32% of the time. While that is a major red flag, it shouldn't be something Red Sox fans should freak out about.

In the past two seasons, Boston’s pitching staff has two prime examples of fixing that exact problem: Aroldis Chapman and Tyron Guerrero. 

In 2024, the season before Chapman joined the Red Sox, his BB% was 14.4, which ranked in the first percentile. The Sox helped him find the strike zone, and in 2025 it dropped to 6.6%. Guerrero spent the 2025 campaign in Japan playing for the Chiba Lotte Marines, where he had a 3.4 BB/9 in 39 ⅔ innings. In 2026, he has a 1.0 BB/9 in 27 innings. 

Andrew Bailey and Co. have found tremendous success helping pitchers with nasty stuff find the strike zone. Everyone thought Chapman’s career was over, and now he’s once again one of the best closers in baseball. Guerrero hadn’t pitched in MLB since 2019, and now he's a trusted late-inning reliever. Miller is already a high-end bullpen piece, but now with the Red Sox coaching staff, he might take the jump to one of baseball’s best. 

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