Analyzing the Fate of Every Red Sox Reliever

The Red Sox’s bullpen has been a bright spot so far in 2025, especially when considering the ongoing struggles of the starting rotation. After finishing 24th in bullpen ERA last season, the Red Sox find themselves 11th through two months of this year's campaign.

Currently, Liam Hendricks, Justin Slaten, and Nick Burdi are all on the 15-day injured list. That leaves a potentially tough set of decisions for Craig Breslow later on in June as to which arms will be sent down to Worcester (or released from the organization entirely). With Richard Fitts being sent back down and Hunter Dobbins regaining a spot in the rotation, the Red Sox will likely keep a starter outside of the bullpen for now. Let's put the current relievers into three tiers determining their safety going forward.

Tier One: Safe

Closer Aroldis Chapman has easily been the best reliever for the Red Sox this season. He leads the bullpen in K%, ERA, and fWAR. Chapman has been everything the Red Sox wanted when they signed him to a one-year deal worth $10.75 million in the offseason. The only uncertainty around Chapman is whether or not he's dealt later on this summer.

Next is Justin Wilson, who has bounced back well after struggling last season with the Reds. Wilson has posted a 2.25 ERA in 20 innings so far with Boston. He currently has his highest K% since 2018, and has elite underlying Statcast numbers which suggest he may not be due for major regression. Overall, Wilson has been a very solid option for Alex Cora in the middle and late innings. Like Chapman, Wilson is a veteran on a one-year contract who could very well be moved come July if the team continues to struggle.

Garrett Whitlock is another arm in the Red Sox’s bullpen who is 100% safe. In 22 games, Whitlock has pitched 31.1 innings, giving the Red Sox some extra length compared to a regular set-up guy. Whitlock is performing nearly identical to his expected stats and is not a major candidate for regression. His slider and changeup have both performed well behind his primary sinker this season, as both pitches are inducing above-average chase and whiff rates. With his potential to give the Red Sox a few extra innings every outing, Whitlock will continue to be a mainstay in the bullpen for the rest of the season.

Although he is injured right now, you can pencil in Justin Slaten to return to the bullpen once he comes off the injured list. Slaten has the best raw stuff out of the pen thanks to his elite extension and run on his pitches. His fastball and cutter continue to dominate, and although Slaten is not working with a great strikeout rate, he consistently spins the ball enough to reduce hard contact. He leads all Red Sox relievers with more than 10 innings in WHIP and BABIP. Expect Slaten’s 3.47 ERA to steadily improve throughout the season once he returns to injury, as his expected ERA is 2.49. If the Red Sox decide to move Chapman at the deadline, Slaten will likely be the guy who gets the ninth inning.

Tier Two: Probably Safe

Starting out the second tier is Brennan Bernardino, who has had an up-and-down career with the Red Sox. Bernardino is a prime candidate for regression through the rest of the season, as he is outperforming most of his expected stats. However, that is simply because Bernardino’s numbers have been elite in 2025. He is second in the bullpen in ERA and WHIP, and has been a reliable left-handed option in the middle innings for Cora. What holds Bernardino back from the first tier is his lackluster stuff. Out of his five pitches, only Bernardino’s curveball has been above average. Ironically, the curveball has given him the most trouble, as it is the only pitch he has given up multiple extra-base hits with this season. I anticipate some eventual struggles for Bernardino at some point in the coming months, but they will likely not be severe enough for him to get sent down.

Greg Weissert finds himself in the second tier, rounding out the six Red Sox relief pitchers with 20 or more innings in 2025. Weissert is having the best season of his career so far, posting a 2.93 ERA and 1.120 WHIP in 27.2 innings. Like Bernardino, Weissert has below-average stuff which keeps him out of tier one. His expected numbers are solid, but Weissert does not induce enough whiffs to be fully regression proof. His sweeper has far and away the best movement profile in his arsenal, but the location has been inconsistent and opponents are slugging 1.000 against it. Overall, he has been a solid option in 2025, and if he can find slightly better location on his sweeper, Weissert could rise to tier one. 

Tier Three: Prime Candidates to be DFA’d or Sent Down

It is safe to say Liam Hendricks has had an ugly start to his Red Sox career. Hendricks was put on the injured list after posting a 6.59 ERA in 13.2 innings. After missing all of 2024, many fans hoped Hendricks would become a reliable late-inning option in the Red Sox’s bullpen. He obviously has fallen well short of that, and will likely be on a short leash when he returns from injury. With his contract expiring after this season, I expect Hendricks to be given another chance out of the bullpen to potentially recapture some value ahead of the trade deadline. Hendricks has actually had above-average stuff this season, and his slider has been easily his most effective pitch. However, when opponents have made contact, the results have been awful. The same has been true for his fastball, but unlike the slider, there has been no swing-and-miss with it. Hendricks has the raw stuff to bounce back, but it is equally likely he will not find a good feel for his location when he returns.

Next is Cooper Criswell, who was just recalled from Triple-A. He has appeared in only four games this season and allowed five runs. Criswell was solid in his 99 innings a season ago, but he now seems like a guy who will mainly stay down in Triple-A as a depth option. With below-average stuff and a below-average track record, Criswell is another likely candidate to be sent down when the bullpen is at full strength.

Zach Kelly is another arm who has struggled mightily this season. Across 13 innings, Kelly has as many runs allowed as strikeouts, and has an ERA over seven. Kelly will continue to be a depth option for the Red Sox, and will continue to split time between Triple-A and the big leagues. 

Luis Guerrero is another arm who has bounced between Boston and Worcester. He has only pitched nine innings in six games with the big club in 2025. He has posted some solid numbers in Boston, specifically a 0.93 ERA. The bad news is that Guerrero’s expected ERA begins with a five, and he has an awful 14.3% walk rate. None of those numbers are sustainable for an MLB reliever. Expect Guerrero to be sent down when Slaten or Hendricks are back from injury. 

Lastly, we have the recently-injured Nick Burdi. Out of the guys with 15 or fewer innings in the Red Sox’s bullpen, Burdi is the only one who has yet to allow a run. Although he only pitched 5 1/3 innings before hitting the injured list, Burdi had an excellent 23.8% K rate. He has never pitched more than ten innings in a big league season, but Burdi could finally surpass that if he gets called back up after returning from injury. He has a legit slider which could be an effective pitch in the majors, and his fastball has been known to hit triple digits in the past. If Burdi can recover well from his injury, I would expect him to get the nod to stay up with the Red Sox over Criswell, Kelly, and Guerrero.