Borussia Dortmund and Hertha Berlin drew 2-2 at the Westfalenstadion on Saturday afternoon but events on the field were overshadowed by violent clashes involving visiting Hertha supporters and local police.
After Hertha ultras ignited pyrotechnics for the second time in the first half, police entered the area in front of the away section and attempted to confiscate a large banner underneath which fans had donned masks - a frequent practice by supporters who don't want to be identified using pyrotechnics, which are banned in German stadiums.
Ahead of kickoff, the same banner had been used as part of an authorized choreography celebrating the 15-year anniversary of the Hertha ultra group "Hauptstadtmafia" (capital city mafia). That choreography also involved the prohibited use of pyrotechnics.
In response to the attempt to confiscate the banner – considered an extreme affront in ultra circles – the ultras attempted to drive the police out of the away end, attacking officers with flagpoles and at least one more flare. In the ensuing melee, police deployed batons and pepper spray against the fans.
According to an official statement from Dortmund police, toilets underneath the away end were heavily damaged at halftime before intervening police officers were again attacked with pieces of porcelain, toilet doors and a metal security fence.
According to the same statement, a total of 45 people were injured during the clashes: 35 by the use of pepper spray and 10 as a result of physical violence. Ten further people are also reported to have been treated after inhaling smoke from the pyrotechnics. Of the injured police officers, all remain fit for duty, added the statement.
As of 20:00 CET, police said that all suspects of wrongdoing had been comprehensively videoed and that they were preparing various charges including disturbance of the peace, resistance to police intervention and illegal use of explosives.
Hertha Berlin released a statement in which they explicitly condemned the use of pyrotechnics inside stadiums. The club also called the violence used against the police "unacceptable" and promised to "take action to identify those responsible."
Hertha's sporting director Michael Preetz added: "This is a day that damages both football and our club. The pyro-orgy was followed by significant physical clashes. It leaves a bitter taste, and not just an aftertaste."
Fans criticize 'disproportionate' police intervention
Meanwhile however, supporter groups have criticized the actions of the police, saying the attempt to confiscate the flag led to an escalation of events.
"An ultra group's flags and other material are considered precious, not just in Berlin," explained fan culture portal Faszination Fankurve afterwards. "Police who attempt to confiscate such material ought to be aware that this can result in an escalation of the situation. An attack on a flag represents the biggest provocation possible."
Berlin-based fan lawyer René Lau tweeted that he had been contacted by Hertha Berlin fans who spoke of an "absolutely disproportionate use of pepper spray and batons" and claimed that injured fans were prevented from leaving the stadium.
Borussia Dortmund fanzine Schwatzgelb said "the police provoked clashes with Hertha fans by confiscating a banner as a result of two flares." Fanhilfe Dortmund, which provides legal aid to football supporters, encouraged Hertha supporters via Twitter to write down their recollections to aid their own investigation.
At the end of the game, police reported that the away supporters were accompanied away from the stadium without any further issues.