It is the coach's job to detect and prohibit such practices, not to administer the system.
How the coaches could fail to get together and come to an understanding that they will not cheap shot the opposition if the opposition agrees not to cheap shot them boggles my mind.
This is why the NHL allows fighting, without allowing it, you would have bounties all the time in hockey. Fighting is the great equalizer. Same in baseball with the brushback pitch...a guarantee that for the most part, pitchers know if they plug somebody, the other team will get revenge.