How did Red Sox LHP prospect, Double-A Portland Pitcher of the Year Hayden Mullins fare in 2025?

Last month, Red Sox prospect Hayden Mullins was recognized as Double-A Portland’s 2025 Pitcher of the Year. This article will examine how the 25-year-old left-hander fared this season.

Mullins broke camp and got the Opening Day nod for High-A Greenville this spring. The lefty posted a 1.06 ERA (1.69 FIP) with 27 strikeouts to just three walks in his first four outings (three starts) and 17 innings of the year before receiving a promotion to Portland in late April. He made his Double-A debut against New Hampshire on May 1 and electrified, striking out 10 (to match a career-high) over 5 2/3 innings of one-run ball.

Unfortunately, Mullins was placed on Portland’s injured list four days later due to shoulder fatigue and did not return to the mound until May 25. He then picked up where he left off by posting a 2.74 ERA (4.33 FIP) with 25 strikeouts to 15 walks in his next six starts (23 innings) for the Sea Dogs through the end of June. On July 1, he threw an immaculate inning against New Hampshire but left the game early with cramps. That led to him making just one more appearance before the MLB All-Star break began on July 14.

Upon returning from the break, Mullins compiled a 2.42 ERA (3.38 FIP) with 53 strikeouts to 26 walks in his final nine starts (44 2/3 innings) of the year. Altogether, he forged a 2.44 ERA (3.79 FIP) with 96 strikeouts to 48 walks over 18 starts (84 2/3 innings) for Portland this season. Opposing hitters in the Eastern League batted .175 against him.

Among 40 pitchers who threw at least 80 innings in the Eastern League this year, Mullins ranked second in batting average against and ERA, third in strikeout rate (27.7 percent), sixth in strikeouts per nine innings (10.2), seventh in swinging-strike rate (13 percent), ninth in WHIP (1.17), 14th in FIP, 17th in xFIP (3.83), and 19th in groundball rate (40.9 percent), per FanGraphs.

Between Greenville and Portland in 2025, Mullins produced a 2.21 ERA (3.44 FIP) with 123 strikeouts to 51 walks across 22 total appearances (21 starts) spanning a career-high 101 2/3 innings of work. In addition to taking home Pitcher of the Year honors for the Sea Dogs, he was named a SoxProspects.com All-Star for the first time.

Mullins was originally selected by the Red Sox in the 12th round (369th overall) of the 2022 draft out of Auburn. The Tennessee native was recovering from Tommy John surgery at the time he signed for $97,500, which pushed his professional debut back until August 2023. Just over two years later, he is ranked as the No. 18, No. 22, and No. 26 prospect in Boston’s farm system by MLB Pipeline, SoxProspects.com, and Baseball America, respectively.

Standing at 6-feet and 194 pounds, Mullins throws from a three-quarters arm slot and incorporates a high leg kick into his deceptive delivery. As noted in his SoxProspects.com scouting report, the undersized southpaw operates with a five-pitch mix that consists of a 92-94 mph fastball that tops out at 95 mph, an 81-85 mph slider, a 78-80 mph curveball, an 81-83 mph changeup, and a mid-80s cutter.

Mullins, who just turned 25 in September, is a candidate to be added to the Red Sox’ 40-man roster next month to prevent him from becoming available to other clubs in December’s Rule 5 Draft. Such a move may be met with criticism since Mullins has yet to pitch above the Double-A level and appears headed for a move to the bullpen given his command and control issues, but his profile could make him an attractive option to a team in need of a bat-missing lefty reliever this winter.

If he remains with the Red Sox through the offseason, Mullins is projected by SoxProspects.com to make the jump to Triple-A Worcester in a relief role to open the 2026 campaign.