Although he has not thrown an MLB pitch in 2020, Robert Stephenson threw 3,563 pitches that were tracked by the PITCHf/x system between 2014 and 2019, including pitches thrown in the MLB Regular Season and Spring Training. In 2019, he relied primarily on his Slider (85mph) and Fourseam Fastball (95mph), also mixing in a Change (87mph). He also rarely threw 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 slight armside run and has slightly above average velo. His change has surprising cut action, generates a high number of swings & misses compared to other pitchers' changeups, 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.