The middle relievers often fly under the radar, yet they play a crucial role in shaping the outcomes of tight games. As the Red Sox gear up for the 2026 season, their bullpen is set to benefit from a strong starting rotation, which should help keep these arms fresh. While the current group may seem a bit light, the unpredictable nature of relief pitching means that opportunities for new talent can arise at any moment. Let’s delve into the pitchers who are vying for a spot in Boston’s bullpen this year.

Justin Slaten had a challenging 2025, largely due to injuries that sidelined him for a significant portion of the season. He finished with a 4.24 ERA, an 18.2% strikeout rate, and a 7.3% walk rate, all of which represented a dip from his rookie year. However, the underlying metrics suggest that his fastball remains a formidable pitch, boasting impressive vertical movement and velocity. His swinging strike rate of 15.6% ranked among the league’s best, and he limited hard contact effectively with his cutter. Slaten struggled to finish off left-handed batters, often leaving his curveball in the strike zone with two strikes. With improved command, he’s poised to reclaim his strikeout prowess. As Aroldis Chapman and Garrett Whitlock lead the bullpen, Slaten will likely find himself in high-leverage situations throughout the season.

Greg Weissert presents an interesting case for manager Alex Cora, who must navigate the middle innings with care. Weissert has consistently been one of the league leaders in appearances early in the season, but his performance tends to decline during the hot summer months before he resurfaces in the fall. He excels against right-handed hitters, utilizing a fastball that he commands effectively at the top of the zone, alongside a sinker and slider/sweeper mix. However, he struggles against lefties, making him best suited for one-inning matchups against right-handed batters.

Meanwhile, Zack Kelly remains a pitcher with tantalizing potential. Averaging 96 mph on his four-seam fastball, he showcases impressive extension, but right-handed hitters have managed to square him up. His approach against righties has yielded a 29.3% strikeout rate, while lefties have been less susceptible, with a 15.7% strikeout rate. Despite some bad luck reflected in his .831 OPS allowed against right-handers, many believe that Kelly could emerge as a vital contributor to the Red Sox bullpen by season’s end.

Ryan Watson, a Rule 5 draft pick, may not be thrust into critical roles immediately, but his ability to throw strikes could earn him more significant opportunities as the season progresses. His pitch arsenal includes a fastball, sinker, slider, and curveball, and he has also introduced a low-90s cutter during spring training. While his minor league performance hasn’t been spectacular, his ability to get batters out could see him rise through the ranks of the bullpen.

Among the non-roster invitees, Kyle Keller stands out due to the Red Sox’s financial commitment to him. Having spent recent seasons in Japan, Keller features a fastball, cutter, and curveball, although his secondary pitches have shown inconsistent results. His performance in spring training will be crucial as he aims to secure a spot on the roster.

Tayron Guerrero is a name to watch, especially after his inspiring journey to the major leagues. Standing at 6-foot-8, Guerrero possesses remarkable velocity but has struggled with command. He features a four-seam and two-seam fastball that can reach 100 mph, coupled with a splitter and a developing gyro-slider. Though unlikely to make the opening day roster, his potential could see him climb the ranks if he can harness his control.

Seth Martinez, who had a solid run with the Marlins, brings a unique side-arm delivery and big extension to the table. His pitch mix includes a sinker, cutter, four-seam fastball, sweeper, and changeup. While his lack of velocity limits his ceiling, his command will be key as he vies for a spot on the team.

Noah Song has made a brief return this spring, showcasing a sharp slider and intriguing fastball movement. Although it may be a long shot for him to make the roster, his potential is undeniable.

Vinny Nittoli, another non-roster invitee, offers a unique look with his low-arm angle cutter. His ability to throw a sinker, changeup, and sweeper could provide a fresh perspective for hitters. Lastly, Devin Sweet presents a contrasting style with his high arm angle, generating significant vertical movement on his fastball. Despite a rocky start to spring training, Sweet’s potential for swing-and-miss stuff makes him an intriguing option.

Note: This recap is an independently written summary based on publicly available reporting.

Richard Hayes is the go-to writer for all things soccer at 21Sports.com. His international perspective and in-depth knowledge of the game have made him a trusted voice in the industry. Richard’s experience covering major leagues around the world allows him to offer unique insights that resonate with both casual fans and die-hard enthusiasts. When not covering matches, Richard enjoys coaching youth soccer in his community.