Green boards outlining proper player conduct are in dressing rooms across the district, as were orange boards on the sidelines for supporters at these games.
Cobb said recent publicity on schoolboy rugby violence was a "nightmare" for both the local and New Zealand union, especially after they were supporting campaigns such as Applaud,, Zip It and recently the New Zealand Herald's Sideline Champs.
"It's an absolute embarrassment to have it happen in our own back yard," he said. "Where's all this aggression coming from? Leave it out of the game, leave it out of your lives. It's a trend we need to nip in the bud."
WHS principal Garry Olver said rugby spokesman and deputy principal Chris Friedel was speaking to the team to find out what happened.
While "niggle" could happen from both sides, that was no excuse, Olver said. "I'm very disappointed, we are making an investigation right now.
"This is clearly a one-off and we will put a stop to it, that's for sure. I won't tolerate this kind of behaviour."
Any disciplinary action and penalties would be the same as if the incidents had occurred during school time, he said.
"Our kids are our ambassadors and when they play for us they represent us."
Olver said he attended three other games rugby, netball and soccer involving WHS teams on Saturday and their behaviour was exemplary.
The Palmerston North head, Dave Bovey, said he would also be speaking to his school's team and coach to try to get to the bottom of what happened before hearing "different versions".
"We certainly don't condone any violence on the field."