https://www.mlb.com/twins/news/twins-call-up-prospect-brusdar-graterol
Though Graterol has been a starter throughout his Minor League career and posted a 5-0 record with a 1.89 ERA for Double-A Pensacola to begin the year, the Twins moved him into a relief role following his recovery from a right shoulder impingement in August. They fast-tracked him to Triple-A Rochester to see if he could be a factor for the Twins in September and brought him up after four appearances for the Red Wings.
So the Twins only transitioned him to relieving because of the injury and the stretch run? That something a lot of teams due to younger pitchers.