You shouldn't stuff someone into a locker.
Will is the star of his high school's football team, and a freshman is talking crap to him.
Will wants to kid to leave him alone.
Will tells the kid that he could fit him in a locker if he wanted to.
Will opens up his locker and pushed the kid inside of it.
The kid doesn't want to risk the chance of being put in a locker, so he walks away.
The kid is scared and doesn't know when he'll be let out.