Sean Doolittle has thrown 4,899 pitches that have been tracked by the PITCHf/x system between 2012 and 2018, including pitches thrown in the MLB Regular Season, the MLB Postseason and Spring Training. In 2018, he has relied primarily on his Fourseam Fastball (95mph), also mixing in a Change (86mph). He also rarely throws a Slider (83mph).
Basic description of 2018 pitches compared to other LHP:
His fourseam fastball generates an extremely high number of swings & misses compared to other pitchers' fourseamers, is straight as an arrow, is blazing fast and has good "rising" action. His change is much firmer than usual and has a lot of backspin. His slider (take this with a grain of salt because he's only thrown 8 of them in 2018) generates an extremely high number of swings & misses compared to other pitchers' sliders, results in more flyballs compared to other pitchers' sliders, has short glove-side cut and has some two-plane movement.