Left-hander Kyle Harrison made his long-awaited Red Sox debut Wednesday afternoon. He did so out of the Boston bullpen, opening the door for Harrison to become an important reliever for the Red Sox the rest of the way. 

Harrison was the big piece acquired by Boston in the team’s surprise blockbuster trade that sent Rafael Devers to the San Francisco Giants in mid-June. The southpaw spent the last three months in the minors, but came out of the bullpen in the sixth inning Wednesday and tossed three scoreless innings against the Athletics in Sacramento. 

Harrison gave the Red Sox a chance to win with his relief work, though Boston lost 5-4 on an uncharacteristic off-day from closer Aroldis Chapman. The young lefty displayed some solid command throughout the outing, as he threw 35 of his 49 pitches for strikes. He didn’t walk anyone as he fanned two batters and scattered three hits in his debut outing for Boston.

Though Harrison started the 2025 season in the big leagues with the Giants, he was assigned to Triple A Worcester when he was acquired by Boston. Alex Cora deployed him as his long reliever Wednesday, but the manager can be flexible with Harrison’s role, after he started a dozen game for the WooSox before he was promoted to Boston.

Could a spot in the rotation be next for the 24-year-old lefty? Or will he continue as an innings-eater out of the ‘pen? The Red Sox have options with Harrison, and the other promising arms we’ve seen over the last few weeks.

Where will Harrison fit with Red Sox the rest of the way?

Young lefties Payton Tolle (who made his third MLB start Wednesday) and Connelly Early (who tied a Red Sox record with 11 strikeouts in his Tuesday debut) both got starts ahead of Harrison for Boston. But it’s unclear if they’ll remain in the rotation, as the team is monitoring (translation: limiting) their workload. 

Tolle has already set a new career high in innings pitched this year, and Early is just a few frames away. To preserve their arms, Harrison could get a few starting nods going forward. Harrison, who is at 102.2 innings pitched this season, threw 124.1 innings for the Giants last season and also went over 100 innings in 2020. He’s shown he can handle such a workload.

Tolle only went two innings on Wednesday because it was the first time he’s ever pitched on four days rest. While he’s set to start next week, his innings will be limited the rest of the way. Early could find himself on a similar innings restriction.

Enter Harrison, who has made 40 starts at the Major League level over his career. The Red Sox had him work on his four-seam fastball while in Worcester, and he’s added a cutter and sinker to his repertoire to go along with a changeup. He put up a 3.75 ERA over his 12 starts for the WooSox. 

At the very least, Harrison could get a start in the final week as the Red Sox try to line up their rotation for the playoffs. But really, the trio of Tolle, Early, Harrison will be auditioning to be a reliable arm out of the bullpen come October and help bridge the gap between the team’s starters (Garret Crochet, Brayan Bello, and Lucas Giolito) and the back end of the ‘pen (Chapman and Garrett Whitlock). 

Any of those young arms could be huge out of the Boston bullpen in the postseason. But for now, they’re showing an early glimpse of the pitching depth the Red Sox could enjoy throughout the 2026 season and beyond.

Matt Geagan

Matthew Geagan is a sports producer for CBS Boston. He has been part of the WBZ sports team for nearly 20 years. He moved over to the web in 2012 and has covered all the highs (and a few lows) in Boston sports.