Dynamo Dresden is in danger of being banned from the German Cup next season following the second case of fan violence in two years.

Rioting broke out during Dresden's second-round loss at Hannover on Wednesday, when 21 fans were arrested and several people were injured, including three police officers.

About 400 Dresden fans overran security to storm into the stadium before kickoff, while about 200 invaded the pitch after the match, setting off banned firecrackers, the dapd news agency reported.

''The stewards were really fearful at times,'' Hannover police spokesman Dirk Hallmann said.

Dresden was originally excluded from this year's competition after supporters clashed with police and rival fans in the second-round match at Borussia Dortmund last season, but the ban was overturned on appeal.

''We've understood the ruling to be a final warning shot,'' Dynamo president Andreas Ritter said at the time, when Dresden was fined ?100,000 ($129,930), ordered to play a home game in an empty stadium and fans were banned from an away match.