Heuer had middling success as Wichita State's No. 1 starter in 2018, leading many scouts to project that he'd fare better as a reliever in pro ball. The White Sox kept him in the rotation for his debut after signing him as a sixth-round pick that summer, then moved him to the bullpen in 2019. His stuff and control improved in shorter stints, enabling him to rocket to Double-A.
After operating with a 92-94 mph fastball as a starter, Heuer now deals in the mid-90s and tops out at 98 with run and sink that produced a 2.1 groundout/airout ratio in his first full pro season. He also has added more bite and power to his mid-80s slider, which has become a solid pitch that neutralizes right-handers. He still occasionally breaks out his changeup, which features some sink.
Heuer exhibited fringy control and command during his days in the rotation but is doing a better job of locating his pitches while coming out of the bullpen. There's some funkiness to his slightly below three-quarters delivery that provides him with deception. If he makes as much progress in his second season as a reliever as he did in his first, he'll probably finish 2020 in Chicago.