For the second year running, the Boston Red Sox bullpen is one of the best units in baseball. Through June 1, pitchers coming out of the Sox 'pen — which includes Brayan Bello pitching after an opener — have combined for a 3.13 ERA. They are a big reason why Boston is in the top 10 in runs against this season.
A rough last two weeks has seen the darker side of the bullpen. The rough stretch has also allowed fans to truly see who is going to be trustworthy this season, and who isn't.
Ranking Red Sox relievers based on how much Chad Tracy can trust them
Honorable Mention: Opener Brayan Bello
Brayan Bello has been pitching in relief every time he comes in after an opener, Red Sox Nation knows he's a starter, though, and he’ll be just an honorable mention because of that. In those outings, he's been fantastic. The righty has posted a 0.71 ERA in 25 ⅓ innings in four appearances after an opener. He has held opponents to a .484 OPS. For the time being, this should be his role.
13. Tyron Guerrero
The 35-year-old ended his almost seven-year hiatus between MLB appearances with the Sox. Unfortunately for the flamethrower, it's been rough. Through his first five outings, he's rocking a 6.75 ERA and a 1.50 WHIP. If he isn't designated for assignment, he’ll be up and down as needed.
12. Alec Gamboa
After a stint in Korea in 2025, Alec Gamboa signed with Boston over the offseason. He made his major league debut in Detroit, a scoreless ninth in which he struck out two before being sent back down to the minor leagues. The Sox have a litany of lefties they can call on, meaning the lefty will likely stay in Worcester unless there are multiple injuries.
11. Eduardo Rivera
The 6’7’’ 23-year-old made an impressive MLB debut against the Yankees. He pitched 3 ⅓ scoreless innings against the Yankees, allowing just one hit and striking out three. Similar to Gamboa, he was sent down after his big league debut and is another depth lefty. There is a scenario where the Sox need a long man in the bullpen, and he can fill that role.
10. Jack Anderson
Another pitcher to make his MLB debut out of the Sox pen this season, Anderson got three longer outings to prove himself to the Red Sox brass. The righty was solid, allowing three runs across eight innings while striking out six. He’ll be a useful depth for Boston this season with his experience from team Great Britain in the World Baseball Classic.
9. Danny Coulombe
Signing halfway into the spring, the veteran lefty was supposed to fill the Justin Willson/Steven Matz role. Unfortunately, the 36-year-old has been extremely underwhelming. Across 16 outings, he has posted just 11 innings and a 6.55 ERA. He has struck out eight while walking six, and twice has been the pitcher to give up the go-ahead run. With other lefties on the major league roster, he is quickly being relegated to low-leverage opportunities.
8. Ryan Watson
The 28-year-old rookie had a very rough first few weeks in the majors. Across his first 10 games, the righty had an 8.10 ERA and walked more than he struck out. Since April 23, he has settled down. In 11 appearances since then, he has 20 ⅓ innings at a 3.54 ERA and has struck out 23 while walking seven. He is mostly relegated to mop-up duty, but he is doing a solid job of eating innings at the end of blowouts and saving the rest of the bullpen.
7. Zack Kelly
Despite currently being in Triple-A, Kelly has actually been having a solid season. In 17 games, the righty had a 3.31 ERA with a 3.63 FIP. The predictive stats like xERA (5.63) and xBA (.289) aren't as favorable. That might be because he allowed inherited runners to score in three of five outings. Kelly has always been up-and-down in Boston, and that doesn’t look to be changing this season.
6. Greg Weissert
Weissert has been one of the biggest disappointments of the season. After posting a sub-3.00 ERA with a heavy workload in 2025, he has a 4.24 ERA in 25 games this season, and that isn’t even the worst of the problem. The righty has entered the game with runners on 13 times this season and seven times — 12 of 21 inherited runners — he has allowed them to score. Eleven times this season, Boston has been worse off after Weissert has pitched than before it. Oddly, of the 12 games he has entered into a clean inning, he has only allowed one earned run.
5. Jovani Morán
The Puerto Rican lefty was mostly unknown to Red Sox Nation coming into 2026. He only made two appearances for the club in 2025 after being acquired from the Twins the previous offseason, but had no real competition at the beginning of camp. Even after the signing of Coulombe, Morán stepped up and has earned his spot on the roster. When he's not used as an opener, Morán has a 1.93 ERA and has struck out 29 in 28 innings. In his three outings as an opener, he has a 15.00 ERA.
4. Tyler Samaniego
With Moran’s struggles as an opener, Chad Tracy tried Tyler Samaniego in that role instead —and it went just as poorly. Against the Guardians, the lefty allowed six hits and four runs in the first inning. That was his worst outing of the year by far, though. The 27-year-old rookie didn’t allow a run in his first 13 career outings. He was touched up for two runs by the Phillies, but in his four outings after that, he didn’t allow a run. Samaniego was not the headliner of the Jhostynxon Garcia-Johan Oviedo trade, but has quickly made a name for himself out of the Sox 'pen.
3. Justin Slaten
Justin Slaten arrived on the scene two seasons ago and quickly established himself as a back-end guy. 2025 wasn’t as dominant due to injuries, but he’s been back to his dominant self this season. While he once again missed some time due to injury, in his 11 appearances so far, he’s only allowed runs in one and is striking out over 12 batters per nine innings. When he comes in with the Sox in the lead, Red Sox Nation can usually bet that they’ll still be in the lead when he leaves.
2. Garrett Whitlock
Garrett Whitlock has quietly become one of the most dominant relievers in baseball. Since the start of 2025, he has a 2.45 ERA and has held opponents to a .562 OPS. The righty has elite chase and strikeout numbers and can pitch more than one inning with repeated success. On most other teams, Whitlock is likely the closer.
1. Aroldis Chapman
When Aroldis Chapman left New York, it seemed as though he was in the twilight of his career. While he was able to win a ring with the Rangers in 2023, he hasn’t been his dominant, All-Star self that he was in the late 2010s for a few years. After he struggled for a year in Pittsburgh, he came to Boston, and all of a sudden, a top five closer in baseball was back.
Since the start of 2025, the lefty’s 1.01 ERA and 0.74 WHIP are the best in baseball among relievers with more than 30 innings pitched. He has held opposing hitters to a staggeringly low .399 OPS, and walked 22 while striking out 110 batters. Chapman has been nails since he joined the Red Sox, and every time he enters in the ninth, he is almost guaranteed to get a save.
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