Borussia Dortmund and Schalke supporters clashed outside the stadium ahead of the Revierderby between the two teams on Saturday.
Around 1,000 Schalke fans arrived in Dortmund and on their way to the Signal-Iduna Park, lit fires and fought with the BVB fans, who also joined them in attacking police who were trying to control the situation.
The police, who used a water cannon to stop Schalke supporters from damaging a fence, said that fans had destroyed a snack bar near the stadium and used the wreckage as missiles,
"Dortmund and Schalke's violent criminals consciously undermined our security concept and arrived ready to conspire," said Dortmund police director Dieter Keil. "Their aim was to fight their rivals and innocent people."
Schalke won the derby 2-1.