Police refused seven people entry after breath-testing visitors as they came through the gates to view one of New Zealand's oldest school rugby fixtures.

30 police officers breath-tested all of the 4000 spectators as they entered Christ College to watch the school take on rivals Christchurch Boys High, only waving school buses through their checkpoint.

A spokesperson for Christchurch Central police said seven people had been turned away from the game, which was won by Christchurch Boys High for the tenth year in a row.

David Rankin told 3 News the move was wrong.

"Why should an elite private school be able to do this with the New Zealand police force?"

Kelvin Victor and John O'Cain told One News they were old boys who had been attending the annual fixture for 60 years.

"It is quite unfair because we're tidy citizens," said Mr Victor.

"I'm not prepared to go," said Mr O'Cain. "Frankly I think it's a bit over the top."

Christchurch Boys High School principal Trevor McIntyre said the schools have been playing each other for the last 122 years but if bad behaviour at the match did not improve, the fixture could be canned.

He said one of the longest standing rugby match-ups in New Zealand's history could not continue to be dogged by bad behaviour so the schools had chosen to take the "extreme" measure of breath testing spectators.

Mr McIntyre said old boys spoke of throwing apples at the opposition and a "cheeky rivalry" between the teams.

"What has been termed cheeky rivalry has, over the last few years, has turned into alcohol fuelled aggressiveness by boys from both schools using it as an excuse for their thuggery," Mr McIntyre said.

He said there had been no problems with students in the last few years and the trouble seemed to happen after the game amongst recent school leavers.

"There's still this culture amongst our recently left old boys that you go and get absolutely tanked and then go to the game and cause absolute mayhem," Mr McIntyre said.

He said there has been some "incredible hype" about this afternoon's match but he is still looking forward to it.

"I'll probably be breath-tested on my way in," Mr McIntyre said before the game.

"The issue is not during the game but after as people move to license premises or other collection points," Mr Erasmus said.

"In the last few years we haven't been able to attend family violence instances and we haven't been able to deal with instances where the public have needed urgent assistance because we're dealing with a bunch of drunken people running amuck," Mr Erasmus said.

He said last year police did a baton charge outside a fast food restaurant after the match and between 10 and 20 people were arrested.

Mr Erasmus said breath-testing at the match was no different from testing at after ball functions and other private school events.