Just as a uniformed police patrol appeared close to the stage, duo Emilush & Caustic began rapping "everybody in Landskrona hates the police" and "we're going to start a war with the cops". The two police officers in question had been tasked with keeping an eye on proceedings at the festival, according to newspaper Helsingborgs Dagblad.
A jubilant crowd is said to have applauded the rappers' sentiments and begun pointing their fingers at the police officers.
Deputy prosecutor Göran Olsson in Helsingborg has now instigated proceedings against the two hip hop artists, whose real names are Emil Göransson (19) and Alexander Nodbring (22).
"Through their actions Göransson and Nodbring displayed contempt for the forces of law and order in a way that was intended to generate disorder among the general public," wrote Olsson in his summons application.
Both of the accused have denied the charges of incitement and disorderly conduct and say they were exercising their right to freedom of speech.
"It is the first time in my 29 years in the job that I have begun proceedings in a case like this. But I think the case should be tried in court," Olssson told Helsingborgs Dagblad.
The prosecutor does not think that the social criticism found in much hip hop music in any way excuses the rappers' behaviour.
"No type of culture has any precedence. I look at the words and the content of the lyrics," said Olsson.
In 1999, one of Sweden's most famous rappers, Ken, encouraged his audience to "go to the palace and rape Princess Madeleine". But the charges brought against him were eventually dropped when he issued an apology.
Per Herrey, a legal expert at the Swedish Musicians Union, struggles to come up with a single case in which opinions expressed in song have led to criminal charges.
"No, I can't remember any case of this kind," he told Helsingborgs Dagblad.