Robert Stephenson has thrown 3,095 pitches that have been tracked by the PITCHf/x system between 2014 and 2019, including pitches thrown in the MLB Regular Season and Spring Training. In 2019, he has relied primarily on his Slider (85mph) and Fourseam Fastball (95mph), also mixing in a Change (87mph). He also rarely throws a Curve (84mph).
Basic description of 2019 pitches compared to other RHP:
His slider generates an extremely high number of swings & misses compared to other pitchers' sliders, results in more flyballs compared to other pitchers' sliders and has some two-plane movement. His fourseam fastball has slightly above average velo. His change generates an extremely high number of swings & misses compared to other pitchers' changeups, has surprising cut action, is much firmer than usual and has a lot of backspin. His curve (take this with a grain of salt because he's only thrown 1 of them in 2019) is thrown extremely hard, is basically never swung at and missed compared to other pitchers' curves, results in more flyballs compared to other pitchers' curves, has little depth and has primarily 12-6 movement.