About 20 to 30 darkly dressed and partially masked people attacked a tattoo studio in Dortmund on Monday.
They damaged a shop window and injured a person in the studio, the police said in the evening.
The group then fled towards the city center.
There was no danger to bystanders.
Dortmund - The police were initially unable to provide any information about the background.
She asks witnesses to report to the police station.