Second division side Dynamo Dresden face tough sanctions from the German Football Federation (DFB) after their fans rioted during a Cup defeat at Hanover 96, a year on from similar trouble at Dortmund.
Violence broke out before the game, which Hanover won 4-3 on penalties following a 1-1 draw after extra-time, as 300 Dynamo fans broke into Hanover's AWD Arena and clashed with police, which held the match up for 15 minutes.
Dresden fans then stormed the pitch after their team's defeat, again forcing police intervention. In total, there were nine injuries while 18 fans were taken into custody.
Only the prescence of 1,000 police officers kept large groups of rival fans apart.
Almost exactly a year ago, Dresden fans were again in hot water after rioting at Borussia Dortmund, which prompted the Federation to slap the east German club with a 100,000-euro ($130,000) fine.
"We were able to deal with the situation, but unfortunately a number of Dynamo fans did not follow police instructions and did nothing to improve their bad image," said Hanover police chief Bernd Kirschning.
With fans chanting hate slogans, burning flares and with bottles flying, one unnamed police officer told German daily Bild: "I have never seen so much aggression at a game. For the first time on duty, I feared for my life".
"The images are shocking," Andreas Rettig, the chief executive of the German Football League (DFL), told broadcaster ZDF after seeing pictures of the violence.
"If that is the perception of a police officer, then that is dramatic. Visiting a stadium is supposed to be safe and pleasant for players, referees and fans. This is not a good development."
Violence at football grounds has caused concern in Germany, after Ruhr rivals Schalke and Dortmund fans clashed on October 20, leading to 180 arrests.
The DFL are planning a security concept -- Secure Stadium Experience -- but several points are proving controversial with the clubs, including proposals for full-body searches and lengthy bans for some fans.
"The paper is not set in stone and will be fully discussed with all stakeholders," said Rettig with clubs holding a summit in Berlin on Thursday.
He added: "99 percent of fans are not involved, because they are peaceful.
"The Herculean task is to separate the fans so that not everyone is sanctioned."