As for who runs the locker room let me let you guys in on a secret - the O Line and D Line run the show in most teams. The star players are the face / vocal ones who are seen by the media but behind the scenes it's the big uglies who run the show. Yeah you get a Peyton Manning, Drew Brees or going back in the day to John Elway who through production / fighting through injury that will garner that respect but typically it's the big uglies who take charge.
Which is one reason why stuff like this happens (among many others) and when you get a bad apple like Incognito it can go horribly wrong.
Our high school had a lineman who was a bully. My son ignored him in gym class for two years. The kid bullied my son for being a wuss baseball and soccer player. Then one day he had enough and beat the crap out of him. The bully went whining to the gym teacher. The gym teacher told the kid he saw nothing. No one in the class saw anything either. Then the gym teacher told my son never do it again.
Your son's gym teacher should be fired for not handling the issue before it got to that stage, and I say that as someone who has a couple of friends who are PE teacher's/coaches who would absolutely have handled it before it came to a physical confrontation between students.
What can a teacher do when a kid is sly enough to pick his spots then lies when kids complain? There's no evidence. My son never complained. As an athlete he didn't want to be labeled. But several other kids had complained to no avail.