Foster turned down the D-backs as a 29th-round pick from an Alabama high school in 2013, spending his next two seasons as a starter at Gulf Coast State (Fla.) JC and a third as a set-up man at Alabama. A 20th-round pick in 2016, he took the first two months of 2017 to attend to personal matters but has made steady progress since. The most effective reliever at Triple-A Charlotte last year, he earned a spot on the 40-man roster in November.
Though Foster primarily worked with a fastball and slider as an amateur, his changeup has become his best pitch in pro ball and helped him limit left-handers to a .198/.249/.288 line in 2018-19. He works with a four-seam fastball that sits at 90-93 mph, peaks at 95 and has some riding life to keep it off barrels. His low-80s slider is the third pitch in his arsenal.
While Foster can't overpower hitters, he's not afraid to challenge them. He consistently throws strikes and has some of the best pitchability among the system's relief prospects. He has the ceiling of a seventh-inning role and should make his big league debut in 2020.