BOSTON — Erik Miller is 6-foot-5 and has a fastball that has reached 99.8 mph this season. Even on modern pitching staffs, that’s a profile that tends to stand out, but when Miller looks around while playing catch these days, he finds himself in awe of others. “There’s some dudes that throw absolute gas,” he said Friday afternoon, laughing. “I’m also maybe like the third-tallest guy. I think the average height in the bullpen is like 6-foot-5, 6-foot-6. It’s insane how big the guys are.”

Boston Red Sox closer Aroldis Chapman is the hardest thrower in MLB history and still regularly hits triple digits as a 38-year-old. Right-hander Tyron Guerrero, who stands 6-foot-8, averages 100 mph on his sinker. The starting staff includes lefties Payton Tolle and Jake Bennett, both of whom are taller than Miller. The group is much more, though, than just a collection of dudes who throw gas.

Three weeks ago, Miller was traded from one of the worst pitching staffs in baseball to one of the best, and he has fit right in. With two strikeouts in a scoreless seventh inning on Friday, he’s up to 14 in 8 1/3 innings and...