Non-MLB
Although they have not thrown an MLB pitch in 2024, Mike Fiers threw 18,798 pitches that were tracked by the PITCHf/x system between 2011 and 2021, including pitches thrown in the MLB Regular Season and Spring Training. In 2021, they relied primarily on their Sinker (87mph), Fourseam Fastball (87mph) and Cutter (84mph), also mixing in a Splitter (82mph) and Curve (72mph).
In 2021, compared to other RHP:
Their sinker is so slow that it is substantially gravitational, is basically never swung at and missed compared to other pitchers' sinkers and results in somewhat more flyballs compared to other pitchers' sinkers. Their fourseam fastball comes in below hitting speed and has some added backspin. Their cutter comes in below hitting speed, results in more flyballs compared to other pitchers' cutters and has strong cutting action. Their splitter (take this with a grain of salt because they've only thrown 18 of them in 2021) is basically never swung at and missed compared to other pitchers' splitters, has an obvious armside fade, has below average velo and results in somewhat more groundballs compared to other pitchers' splitters. Their curve (take this with a grain of salt because they've only thrown 12 of them in 2021) has an exceptional bite, comes in below hitting speed, is basically never swung at and missed compared to other pitchers' curves, results in more flyballs compared to other pitchers' curves and has slight glove-side movement.