Alyson Footer likes J.R. Towles for C1 to open the season. Why?
When Spring Training opened, the Astros were hopeful that he'd give them every reason to give him another chance to prove he can be an effective Major League catcher. They always liked his work behind the plate; all he had to do was hit well. He has.
Castro is the catcher of the future and his time is coming. But the only reason the Astros had to rush him to the big leagues was if no one else stepped up to show they could handle the starting job. Towles might struggle at some point which could clear a path for Castro, but right now, having Castro open the season at Triple-A, where he's never played, isn't a bad idea.
Also, another excellent reason:
Another issue is roster space. Should he make the team, Castro would first have to be added to the 40-man, which currently stands at 39. That could be problematic, considering the front-runner to win the fifth outfielder position is Cory Sullivan, who would also need to be added to the 40-man. The addition of both Castro and Sullivan would necessitate taking someone off the roster, but if it's not a dire situation, why do it?
+1 to Footer. Excellent points.