I assume the OP is completely unaware of "head hunting" in professional sports. An awful practice still subtly used today.

Story Time:

I play beer league/pick-up hockey as an adult, and we once had a suspected thief that was stealing from others in the locker rooms during pick-up games. It was believed said thief would get dressed with everyone, and would then "accidentally forget something" before his shift was up, and he would then return to the locker rooms when the rooms were unattended and proceed to shift through people's belongings.

After some time and some mob mentality, people managed to figure out who the thief was. I heard numerous instances of all the various plots and methods other players were working on to ensure this guy would never be able to play again due to an unfortunate accident (i.e. premeditated and intentional permanent or long-term injuries).

Thankfully, the police got ahold of the thief before any of the psychopaths managed to ruin the life of the thief and their own lives. I am also thankful that I was a goalie, so that I was never encouraged to participate in such barbarianism. I value the safety of another person more than a wallet full of replaceable items.

Still, there have been instances where police have been called due to unruly players and/or unruly parents of children players, refs being assaulted by players/parents, etc..

I've never seen that although I'm sure it happens. What I have seen a lot is the entire crowd cheering when a visiting player is able to walk off after being knocked down with a possible injury.