Right-hander Zack Kelly is headed for free agency at age 31 after clearing waivers, closing his five-season career with the Boston Red Sox, the only big league team he’s ever known.
Boston designated Kelly for assignment Monday, and the open question is who signs a reliever with a mid- to upper-90s fastball and an elbow that ended his 2026 season.
The Red Sox needed room on the 40-man roster ahead of the offseason deadline. Kelly came off it along with left-hander Eduardo Rivera, who was later traded to the St. Louis Cardinals. Kelly cleared waivers by Friday, and a “strong market” is anticipated once he officially becomes a free agent, according to MassLive reporter Chris Cotillo.
Contract status forced the issue. Kelly is out of minor league options for 2027, so Boston could no longer shuttle him to Triple-A Worcester. He is also arbitration-eligible for the first time, with a projected salary between $800,000 and $1 million, according to Boston Sports Journal. The club explored trades before the designation.
Zack Kelly’s Road to the Boston Red Sox
Kelly, a 6-foot-3, 231-pound right-hander, was born March 3, 1995, in Roanoke, Virginia, and pitched at Newberry College. No team drafted him in 2017. The Oakland Athletics signed him with a $500 bonus and released him in 2018.
The Los Angeles Angels signed him next. He climbed to Double-A, but the Angels released him in 2020 during the COVID-19 shutdown, following elbow surgery. The Red Sox signed him to a minor league contract on Jan. 4, 2021. Strong 2021 numbers at Double-A Portland and Triple-A Worcester earned a non-roster invitation in 2022, and he debuted Aug. 29, 2022, against the Minnesota Twins.
All of his major league work has come in a Boston uniform. Kelly is 8-8 with a 4.04 ERA and 127 strikeouts in 131⅓ innings over 115 appearances, only three of them starts. His best season came in 2024, when he made 49 appearances, posted a 3.97 ERA and landed on the postseason roster. In 2026, he went 0-2 with a 3.31 ERA in 17 games before the injury.
Elbow trouble dominates his medical file. He had internal brace surgery on his ulnar collateral ligament in 2020. Elbow inflammation in April 2023 sent him to the 60-day injured list and led to ulnar nerve transposition revision surgery by Dr. Jeffrey Dugas. He returned in late September.
The 2026 problem was a stress reaction in the olecranon bone of his elbow, later reported as a fracture. Boston optioned him to Worcester in May, he went on the minor league injured list in early July, and he moved to the major league 60-day list July 21, according to MLB Trade Rumors.
Zack Kelly’s Free Agent Market
Kelly works mostly in the middle innings, with an occasional turn as an opener or multi-inning option. Boston deployed him in lower-to-middle leverage situations.
His repertoire leans on the cutter. In 2026, he threw his cutter 43.8% of the time, averaging 90.6 mph. The sweeper followed at 21.9% and 81.6 mph. His sinker (17%) averaged 95.9 mph and topped out near 98, his four-seam fastball (13.8%) sat at 96.1 mph, and a changeup (3.5%) averaged 83.6 mph.
That velocity, the five-pitch mix and the modest price are what drive the interest, according to Cotillo. Kelly is expected to draw interest around the league, and the recovery from the elbow injury is the main variable. He is expected to be healthy enough to contribute in 2027.
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