Clearly convey expectations during recruiting.
We're paying for your school - we expect basic adherance and respect of team rules and attendance, and work ethic at practice.
I'd give one warning.
Second time - benched.
3rd time - suspended.
If it continues they likely lose scholarship.
The coach cannot allow disrespect like that. Walking out of practice- if done in anger/frustration - is a sign of immaturity and is disrespecting teammates coaches and ultimately the school and fans. It cant be tolerated regardless of who the player is.