The brawl erupted in the last minute of the secondary schools first XV game between Kelston Boys High and Auckland Grammar on Saturday, which Grammar won 20-9.
Players and up to 100 spectators were involved.
Grammar headmaster John Morris said a Kelston player took to one of his players with a "king hit" out of frustration following a try.
But Kelston principal Steve Watt says the footage clearly showed one of his players being punched twice by a Grammar pupil before the try was scored.
Mr Watt said he would be calling Mr Morris this morning.
Both said they were reviewing footage of the brawl before deciding on any disciplinary action.
Footage from the attack shows players punching each other in several smaller fights and then a woman, who TV3 said was a parent, trying to intervene.
Auckland police Inspector Willie Taylor confirmed an investigation was under way.
But he said he was not yet aware of any complaints stemming from the brawl.
Manoj Daji, chief executive of College Sports, the body representing high school sports, believed there had been an increase in such incidents this year.
"With what's happening in society in terms of the recession, there's a lot of tension.
"It's mainly adults behaving badly ... I think some of that tension is spilling over into a place where they feel there's going to be no consequences for them.
"We take a hard line on it. We're in a situation in New Zealand where we haven't got lots of volunteers or officials.
"Officials are sacrosanct. We need to look after them and protect them and keep them in the game."
New Zealand Secondary Schools Rugby Union secretary Alex Bing, who witnessed the brawl, said the issue was not with the players but with spectators.
"If people hadn't come across [the field], I'm sure the whole thing would have died off within half a minute.
"The problem we have is around spectators coming on the field.
If they come en masse, what can you do about it unless you've got security there?"
Asked whether there were plans to step up security, Mr Bing said: "The problem we've got is cost. Who's going to pay for it? The schools can't afford it."
Auckland Rugby Union chief executive Andy Dalton will this morning review a full referee's report of the brawl.
He said it was likely both teams would appear before a judiciary early this week.
Details have also emerged about a violent incident at the other semifinal match.
Spencer Fletcher, a 19-year-old spectator, was hit in the face with a rock at the game between St Peters College and Mt Albert Grammar, which Mt Albert won 17-16.
Mt Albert Grammar headmaster Dale Burden said he was trying to find witnesses to the rock-throwing incident, but did not know which team the attacker supported.
He said he had no concerns about playing Auckland Grammar in the competition's final at Eden Park this weekend.
"In Auckland, every week, there's just thousands of games played in good spirit. It's pretty unlikely that anything will happen next week."
Sports bodies say there has been a significant rise in the number of sideline incidents this year - but most have involved adult spectators abusing officials and referees.
A witness to the rock attack, who asked not to be named, said he was standing with his 3-year-old son on his shoulders, watching a haka following the match, when he heard a "soft thud".
"This rock came flying into the crowd and hit the chap who was one metre in front of me," he said.
"It just hit him smack in the face. It was just awful."
- The New Zealand Herald
