What Red Sox Are Getting In Reliever Steven Matz

The Boston Red Sox made their first move of trade deadline season when they acquired Steven Matz from the St. Louis Cardinals on Wednesday.

Matz, 34, has worked primarily out of the Cardinals’ bullpen this season. His outings typically range between one and two innings, though he’s made some longer appearances when necessary.

The lefty has been excellent against left-handed hitters this season. He uses a sinker/curveball combination against them, and it’s held them to a .442 OPS.

He uses the sinker about two-thirds of the time to lefties, and they’re yet to figure it out. It features solid velocity at about 95 mph and plenty of horizontal run. Matz prefers to throw it back door and spots it well, leading to an absurd 30% called strike rate. While he doesn’t miss a ton of bats with it, it’s rarely ever barreled up and has just a .220 average against it.

The curveball is solid as well. It’s used both in and out of the strike zone for called strikes and whiffs. It’s much slower than the sinker at 79 mph, and the difference in velocity helps keep hitters off balance. The curveball has registered a huge 59% groundball rate against lefties, who are hitting just .103 against it.

Righties have given Matz more problems. In 138 plate appearances in 2025, right-handed hitters have an .814 OPS against the Red Sox’s new reliever. He still uses both the sinker and curveball against righties, but also features a changeup about 27% of the time.

The sinker has been okay. It returns strikes at a high rate, but it’s been hit hard at times. The curveball is his third offering against righties, but he’s left it over the plate too often, resulting in a .313 average against it. The changeup hasn’t performed well, but there are reasons to believe it might.

Righties have hit .333 against Matz’s changeup this season, but that might not hold. The quality of contact against the pitch hasn’t been very good. The ideal contact rate is low at 27.8% and the expected batting average of .239 is well below the actual average.

He’s allowing too many balls in play, but he could increase his whiff rate by being out of the zone more often. His chase rate is very high at nearly 40%, but a high zone rate limits the number of swings and misses Matz generates.

Working out of the zone with his changeup more often could help Matz’s performance against righties, even if he does hand out a few additional free passes. If he can do that, he could become a potential multi-inning weapon in the Boston bullpen.