The police had been called to a parking lot near the stadium because hoodlums would attack other fans there.
However, the officers did not meet hoodlums, police said on Saturday afternoon, but four injured fans, including one seriously injured.
These belonged to both the Cologne and the Hoffenheim fan scene. The tangible argument was probably preceded by a verbal dispute, as the police said.
In the Cologne stadium, paramedics provided a heavily injured man who had fallen over a balustrade after the final whistle.
Another man had to be treated as a medical emergency. While the rescuers cared for the injured, unknown persons stepped off the side mirror of the ambulance.
After the fourth defeat in Serie KOln remains with seven points in 17th place in the table.