The Rockies are set to promote pitching prospect Sean Sullivan, according to Kevin Henry of the Denver Gazette. Sullivan will start tonight against the Athletics and make his major league debut in the process. The lefty is not on Colorado’s 40-man roster, which is currently full. Thus, a corresponding move will be needed in order to select Sullivan’s contract.
Sullivan, 23, was the Rockies’ second-round draft pick in the 2023 draft. He currently ranks as the organization’s No. 11 prospect, according to MLB.com. Sullivan fared well in 20 starts between Single-A and Double-A last year, posting a 2.94 ERA in 104 innings with a 24.9% strikeout rate. He’s been less fortunate in 2026, with a 5.60 ERA in 11 starts at Triple-A.
The 6’4″ Sullivan is a bit of an oddity in terms of his raw stuff. He throws a four-seamer 41.0% of the time, but the pitch only averages 89.0 MPH. Sullivan mixes in an upper-70s slider 29.9% of the time, plus a changeup and cutter at 14-15% each. The changeup is Sullivan’s best pitch, while scouting reports rate his fastball and slider as slightly below-average. Despite the low velocity, Sullivan generally thrives by leveraging pinpoint control and a deceptive, low three-quarters arm slot (video courtesy of MLB.com). He walked just 6.0% of hitters in the minors last year and has walked 7.7% of hitters at Triple-A in 2026.
Sullivan will now have a chance to prove himself in the big leagues as a control and deception guy. Tonight’s game is at Las Vegas Ballpark, the hitter-friendly home of the Athletics’ Triple-A affiliate. If he sticks around for multiple starts, Sullivan could then try his luck at high altitude, with the Rockies hosting the Red Sox at Coors Field from June 22-24.
Rockies starters have performed poorly in 2026, as is seemingly the case every year. The rotation’s 5.94 ERA is dead last in the Majors and 26% worse than average even accounting for the games at Coors. No Rockies starter has thrown enough innings to qualify, with Tomoyuki Sugano just barely missing the cut at 68 1/3 innings. Sugano’s 4.08 ERA is palatable but well shy of his 7.39 xERA, which shows he’s been extremely lucky. Michael Lorenzen and Kyle Freeland are the only others to throw at least 50 innings. Both have ERAs over 7.50.
Given those underwhelming performances and injuries to other starts, there’s little harm in calling up Sullivan. Chase Dollander, one of the team’s more promising arms, has been out with a right elbow sprain for over a month and is not expected to return soon. Tanner Gordon made two starts at the end of May before landing on the 15-day injured list with a right hip impingement retroactive to June 2nd. He’s expected to throw a bullpen soon. FanGraphs’ RosterResource tool currently has the club at a four-man rotation of Lorenzen, Ryan Feltner, Freeland, and Sugano, so Sullivan can serve as the fifth starter until Gordon returns.
Photo courtesy of Rick Scuteri, Imagn Images
