Role
Rivera is a 6'7" lefty from Puerto Rico who signed with Boston as a minor-league free agent in June 2024. He pitched 3.1 scoreless innings against the Yankees in his April 22 debut and made three starts in July. His season ended on Sept. 1, when Boston moved him to the 60-day IL with a lumbar strain.
Outlook
There isn't much big-league data yet: 10 innings, 10 strikeouts, 6 walks, and a 6.30 ERA that mostly comes from a July 22 start in Baltimore where he got two outs. He was better at Worcester (2.96 ERA, 55 strikeouts in 45.2 innings), though he walked 27. His fastball averaged 95.3 mph per Statcast. He also spent four days on the restricted list in August (Aug. 17 to 21, per MLB transactions).
Our take: he's 23, left-handed, and throws 95, which is why he's on the 40-man. Walks and the back injury are the questions for 2027.