Athletes and cheerleaders at universities are allowed to be members of their teams if they adhere to the rules and regulations of the team. If they are caught drinking, have poor grades, offend the coaches, disrupt university functions, or do anything else that displeases the university they can be kicked of the team or squad at any time. This is not about their "constitutional rights" -- they can protest anyway they want on their own time but this does not mean they will represent the university by being a member of a team or squad at public events.
Do you have the "constitutional right" in the workplace to disrespect the flag on company time in their office and expect not to get fired? The answer is no.
All fine and dandy until you have state reps and sheriffs asking for it