While there was a consensus the problem did not reach the heights of last year's rioting, when police arrested 69 people, police again donned riot gear and carried shields to clear missile-throwing people from Castle St. They made 30 arrests.
Dunedin area police commander Inspector Dave Campbell said few Canterbury students were among the 300-strong crowd police faced.
"I don't know that we can blame Canterbury students for this one. We may have to look at Otago students this time."
Fires lit in the streets sparked the disorder, after a day's drinking after the arrival of about 40 unofficial Undie 500 vehicles from Christchurch.
The "official" version, run by the University of Canterbury Engineering Students Society (Ensoc), was cancelled after last year's problems.
About 100 extra police were in the city from Invercargill and Christchurch to support the Dunedin area officers.
The Fire Service attended three fires related to campus-area activities on Friday night. While two were minor, a third attracted a large crowd, though that quickly dispersed when police and fire crews arrived.
Saturday began quietly, and Insp Campbell said a rugby match between Ensoc members and Otago students was "very well behaved".
Officers spoken to on the beat earlier in the day said students had been good-natured, most just taking advantage of the sun to drink in front of their flats.
Students from Canterbury said they were looking to have a low-key night so that the official Undie 500 could return next year.
Police increased their attention about 6pm, foot patrols and patrol cars providing a "constant presence" on the streets. Campus Watch was also patroling.
A temporary liquor ban put in place by the Dunedin City Council had been working, but as people left the Gardens Tavern, they went to flats and got bottles and rocks, Insp Campbell said.
Police were unable to contain those who gathered on Castle St to watch a couch fire set about 11.50pm, just as more young people poured from the Gardens Tavern.
About 30 minutes later, officers donned riot gear as they worked to clear the street.
When a police skirmish line was set up around the fire, people started dancing in the street, chanting and throwing bottles at police. The skirmish line created a tense and heated situation.
Police in full riot gear walked towards the group, who continued to jeer and throw bottles at the police line.
Anyone caught up in the skirmish line was arrested, including a reporter from the university student magazine Critic, who was trying to take photographs of police.
Police ran in lines from three vans to replenish staff on the skirmish line, which advanced three times on the crowd of about 300, before it dispersed about 2am yesterday.
On Saturday night, Insp Campbell said he was "thoroughly disappointed" by what had happened.
"We thought the situation was under control: the day had gone quietly, it was pretty low-key, everyone was well behaved. This [the disorder that followed] was definitely unexpected."
• Arrests by numbers
Friday night: 5
Canterbury University students: 3
Otago University students: 2
Saturday night:30
Non-students: 13
Otago University students: 12
Canterbury University students: 3
Otago Polytechnic students: 2
Arrests were for: Obstruction; disorderly behaviour; breaches of the peace; breaches of liquor ban.
Most bailed to appear in Dunedin District Court on Thursday.
- Additional reporting by Debbie Porteous.
