Castro has four strikeouts and only one hit allowed in three innings this spring.
The 21-year-old is competing for a bullpen spot with Colorado, and he's certainly making a strong case to get one of the last spots. He pitched a bit in the majors last season, but saw little success as he posted a 6.11 ERA in 17.2 innings between the Rockies and Blue Jays. There is a chance that he can crack the 25-man roster if he continues to pitch well, but he could also head back to the minors if the Rockies choose to have him face more advanced hitters prior to being a full-time member of the major league club.