As for the locker, yeah, if there was no communication whatsoever, then that is a pretty dramatic step. Whether it is a cop movie or a sports movie you frequently hear the "clear out your locker" line. I can remember our HS football coach using that as the challenge to the team "if you don't like it, clear out your locker and quit". I have a friend who is a D1 head coach in another sport, I'll ask him what he thinks about the locker thing. I will say that I won't be surprised if we find out that previously Parker had told him that one more occurrence and he was off the team, or something to that effect.
The locker is the property of the school and I don't think it is unprofessional to clean it out if you have decided the player is off the team. They aren't allowed in the locker room if they aren't on the team so their stuff shouldn't be in there. I could hear the whining if he made the player go in there in front of his teammates and clear out his locker. It is absolutely not unusual for a company to tell a dismissed employee that they will clear the desk/office, collect the personal effects and either deliver them or make them available through HR. Once you are terminated for cause, you have no right to return to the desk and the company has the obligation to protect its current employees and also not allow unauthorized people to enter the workplace. In some situations the person is escorted to the desk but that often brings claims of being intentionally embarrassing. And no, it is not incumbent on the team or a company to make the workplace available off hours so the person can retrieve their stuff.
If Glass had no idea he was on thin ice, had no previous issues and had never been given any feedback to straighten up, then it would be a gross over-reaction. If, at the end of this we hear that is the case I will absolutely say Parker's action was not proportionate. However, I think we all know that wasn't the case.