Police say they are not trying to stop Rugby World Cup fans from enjoying themselves at games but say Mexican waves which sweep around crowded grounds can lead to problems.
Rugby fans often got the urge to throw things onto the field during Mexican waves, said Dunedin police and they would "clamp down on these at the point of origin", said police in the latest issue of the police magazine Ten One.
Dunedin police said parts of the new Dunedin stadium were only six metres from the playing field, making it easy to throw things onto the field.
"Fans often get the urge to do this during Mexican waves," said Inspector Al Dickie, of Dunedin police.
"If there is any nonsense we plan to deal with it quickly and firmly and make sure it doesn't get out of hand," he said in the magazine.
However, police later issued statement saying they wanted to clarify what they meant.
Mr Dickie said police were not banning Mexican waves at Dunedin's new stadium.
Police were concerned about any behaviour that might endanger the safety of others.
"Our concern is about objects being thrown into the air that might compromise the safety of others. We do want people to enjoy themselves and have a good time within the bounds of the law, while being mindful of the safety of others around them," he said in the statement.
The new stadium was due to be completed in August and would host the first of four World Cup matches on September 10.
Because of stringent health and safety measures around the stadium during construction, police familiarisation visits had been limited.
Mr Dickie said two Otago matches in August would allow police to practise their policies before the World Cup.
The six-metre gap between the perimeter fence and the playing field was a "stand-out characteristic" of the stadium, while the steepness of the North Stand could also "be challenging in the event of arrests", he said.
Carisbrook, the city's main sporting venue since 1873, was the backup for the new stadium. At 30,000 it had a similar capacity to the new stadium and police had developed plans for both venues, although the use of Carisbrook was "becoming increasingly remote", Mr Dickie said.
Police numbers for the games would be swelled by Maori wardens, up to 70 members of community patrols and 350 volunteer guides.