Role
Boston got Miller from the Giants at the Aug. 3 deadline, with outfield prospect Carlos Gutierrez, and gave up Marcelo Mayer. He pitched late innings right away, mostly ahead of Aroldis Chapman, and Boston.com reported that he's under team control through 2029. He opens 2027 as the club's main left-handed setup man.
Outlook
Miller misses bats. Hitters whiffed on 34.8% of their swings against him in 2026 per Statcast, and his slider (about 41% of his pitches) drew a 53.1% whiff rate. He had 74 strikeouts in 51.1 innings across both teams. The walks are the catch: 34 on the season. His Boston stint ran hot and cold. He posted a 0.79 ERA in August with 20 strikeouts and 3 walks, then a 7.36 ERA with 9 walks in 7.1 innings in September. In the Wild Card Series he got two outs and gave up four hits. He also spent time on the IL in both 2025 (elbow) and 2026 (back).
Our take: Mayer was a lot to give up for a reliever. The control decides whether the deal looks fine in a year. We think the August version shows up more often than the September one.