Fights broke out between Borussia Dortmund fans and suspected touts as the remaining tickets for the club's Champions League semi-final first leg against Real Madrid went on sale.
A limited number of extra tickets became available on Tuesday morning at several locations around the city, with hundreds of supporters camping out for up to two nights in hope of snapping up the last few.
According to local newspaper Ruhr Nachrichten, police were forced to stop the fighting at the various kiosks after suspected touts sent their own people to try and jump into the queues for them.
"Dortmund fans are passionate, emotional and this club is marked by something unusual," said fan Daniel Schrader, who spent two nights waiting in line.
Dortmund CEO Hans-Joachim Watzke admitted the club made a mistake by offering tickets on the open market.
"We underestimated the run on the tickets," he said in a statement. "We will draw our lessons and will not have a free sale like this again."
The Bundesliga club refused to state how many extra tickets went on sale but with each supporter able to purchase two, many were left empty-handed.
All 66,829 available tickets for the April 24 clash have now sold out. The Westfalenstadion usually accommodates up to 80,000 spectators but is reduced for European games as standing areas are not prohibited.