Just finished watching a short scouting video on Kohl Stewart
His unusual velocity comes from a very efficient, tight rotation of his forearm as he turns his shoulders. As I watched the video, two other things stood out: First, he barely even flexes the knee of his drive leg. Talk about effortless, he's hardly using his thigh and calf muscles. Second, like a lot of young pitchers, Stewart is far more precise when he pitches from the stretch than from the windup. Frankly, from the windup right now he would have a terrible time walking batters, because he scatters pitches all around the zone. Kohl Stewart is extremely raw, like converting a shortstop with a great arm into a pitcher. However, unlike a typical shortstop, Stewart's delivery is almost magically efficient, like Matt Moore or Matt Harvey. High release point, steep downward plane, very low expenditure of energy to launch a baseball at 95mph. This means he could potentially throw a lot of pitches before he starts losing control through fatigue. So yeah, Kohl Stewart does project as an eventual starting pitcher, possibly a great one. But his greatness will come from learning how to be a pitcher in the Twins minor league system, because right now he's a thrower, and from the windup he'd walk about ten guys per game.