An all-in brawl forced a rugby match between St Edmund's College and Marist College to be abandoned at Canberra Stadium last night.

The under-18 division one ACT Junior Rugby Union grand final between two of Canberra's most prestigious rugby schools erupted into violence midway through the second half.

St Edmund's held a comfortable lead at the time and it is unknown how the fight began.

At least two players, one from each side, were sent off and an undetermined number also sin-binned for their role in the fracas.

In an unprecedented move, ACT Junior Rugby Union president Martin Sullivan then intervened, walking on to the field and speaking to the referee before abandoning the match.

Matches between the great rivals are always hotly contested and a number of minor scuffles were reported earlier in the contest.

According to witnesses, there was tension between opposing supporters in the grandstand with security guards forced to intervene after a missile narrowly missed a group.

Both schools declined to comment when contacted by The Canberra Times yesterday, but it is understood the incident will be investigated at a school level as well as by the ACT Junior Rugby Union.

Sullivan confirmed yesterday there was an altercation but would not comment further.

''There was a very disappointing end to the under-18 [division] ones game, there was a bit of a melee,'' Sullivan said.

''We've got a judiciary process and that will be followed ... we don't want to jeopardise the judiciary ... so we won't be making any comment on it.

''At the end of the day the judiciary is a full process, we've got older, experienced rugby players that sit there to actually educate and teach the boys the right way of doing things.

''We want to make sure the boys understand what's happening and go through the judicial process.''

Sullivan said the referee's report would be among evidence handed to the judiciary when it sat on Wednesday night.