In Jake Arrieta’s first start of the 2017 campaign, he averaged 90.5 mph, down from his typical 94 mph average. Even more unsettling, the switch to Trackman data means the 90.5 MPH average might have read like 89.5-90 mph with PitchFX tracking. It’s possible the bearded Cubs pitcher was essentially throwing over 4 mph slower in his first start than he was last season.
To preface, let me say that I’m skeptical about his data from Busch Stadium. The tracking was very spotty and only half of Arrieta’s pitches were recorded for some reason.