The concerns follow an incident on Sunday, in which two 17-year-olds chased a third with whom they were arguing, into a central city food outlet and beat him until he required hospital treatment.
That sort of group-on-one situation was "unfortunately" becoming increasingly common in Dunedin, Dunedin-Clutha police area commander Inspector Dave Campbell said yesterday.
Groups of young men and women would congregate in the central city streets, usually at night, and at least one of them, without provocation, would assault a stranger.
"I've got no idea why they want to do it, but for whatever reason young people are spoiling for a fight and want to punch people."
Offenders tended to pick on people clearly affected by alcohol.
People who had had too much to drink often made unwise decisions, such as reacting to taunts, or being unable to judge when to avoid groups they might otherwise recognise as looking for a fight, Insp Campbell said.
His advice to people going out in the city was to stay with their friends and avoid groups of people who appeared to be looking for trouble.
Young people who did assault others also received a clear warning from a Dunedin District Court judge last month.
Sentencing high school pupil Tyrone Smith (17), Judge Stephen Coyle said street thuggery was happening far too often in the city.
Smith was sentenced to 120 hours' community work after he pleaded guilty to punching a man he did not know, when the man walked past him in George St on August 22.
Smith had been in the street with a group of friends when the victim and his girlfriend walked past.
When the victim did not respond to verbal taunts, Smith punched him in the head.
Judge Coyle told Smith young men like him went into town thinking it was appropriate to "thump" anyone who looked at them the wrong way or whom they did not like the look of.
"Well, that is absolute bollocks.
"I do not know if you think you prove your manhood by thumping innocent members of the public, but the court is not going to tolerate it, and society certainly doesn't tolerate it.
"It is simple, basic thuggery and it is nothing to be proud of at all."
Prosecutor Sergeant Paul Knox told the judge this type of situation - where young men like Smith went out with "gangs of mates" and were "just looking for a scrap" - was repeated often in central Dunedin.
"And it's rather tiresome as far as police are concerned."
Judge Coyle said young people would pay the price if they were going to behave like that.
"People will end up doing more and more community work until the young people of this city start behaving responsibly."
Insp Campbell said police welcomed and appreciated that support from the courts.
