Players play at the discretion of head coach. Punishment or not, the head coach owes no one an explanaiton of why he does or does not choose to play someone. Every team has rules. If you choose to be a part of that team you choose to abide by those rules. Those team rules have absolutely NOTHING to do with any kind of constitutional rights. Everyone has the RIGHT to stay out until 2AM before game day, but if that is a violation of team rules then you will most likely sit. If coach thinks it is a bad idea for players to carry fire arms - that is within his authority to make that a team rule. A football team is not a democracy.
I doubt you're going to have a team rule that says you can't legally carry a gun. That's why Alabama doesn't have one.
You may have a team rule about getting arrested, but that covers anything and everything. You can't punish him legally carrying a gun. You can only punish him for getting arrested and not following the law.
Saban can punish him for breaking the law and getting arrested, but I will stand behind this young man until the bitter end regarding his rights. They're more important.