Christ's College and Christchurch Boys' High School have decided to breath-test every spectator turning up for their annual interschool fixture later this month, 3 News reported this week.
The match has a chequered history.
Old boys of the two schools have clashed on the sidelines, and police have been called in recent years.
Now the schools want to put the focus on what is happening on the paddock, and have decided everyone will be breath-tested when they enter Christ's College for the game on June 22.
Christchurch Boys' High School principal Trevor McIntyre said it did not matter whether spectators were aged 8 or 80 - they would be breath-tested for alcohol.
If they were found to be drinking, they would be refused entry.
Christ's College is sited in a liquor-free zone and police say it will be strictly enforced.
More than 3000 have been at the match over the past few years.
Originally, the plan had been to bar anyone aged under 22 from watching, as most of the trouble had been caused by past pupils.
Kaikorai Valley College deputy principal Garry Chronican, who is also the chairman of the New Zealand Secondary Schools Rugby Council, said such incidents had never happened on the sidelines of school rugby in Dunedin.
There was perhaps not the intense rivalry between schools in the south that existed in Christchurch, and spectators were well behaved.
He thought the move to breath-testing was a good move in the short term and switched the focus on to the game.
There had been too much "stupid stuff" on the sidelines, which had overtaken the game on the field.
King's High School principal Dan Reddiex said the school had a healthy rivalry with Otago Boys' High School but it never went too far.
There were no incidents off the field and players, both past and present, were mates off the field, he said.
King's will play Otago Boys' in the traditional interschool on July 2, the same day as Waitaki Boy's High School plays St Kevin's College in Oamaru.
