According to the security authorities, the rushing of football fans after the games of 1. FC Köln and FC Schalke 04 could have had dramatic consequences.
Above all, the boundless cheering in the arena in Gelsenkirchen presented the police with a major challenge.
"This space storm could have ended in a catastrophe," said Chief Police Director Peter Both.
Both clubs face consequences.
The control committee of the German Football Association has started investigations after the incidents on Saturday, as a DFB spokesman confirmed on Monday.
The clubs were asked to comment.
Nine seriously injured
According to current knowledge, 18 people were injured in Gelsenkirchen, nine of them seriously.
Nobody is in mortal danger.
"Thanks to the immediate and quick intervention of numerous police officers, it was possible to prevent anything worse from happening here," said Both.
More than 2,000 fans crowded onto the field, and there were falls and injuries in the stands.
Some victims were taken to the hospital.
Lawn no longer playable
"We hope that people will recover quickly and wish the injured a speedy recovery," said a spokesman for FC Schalke.
The crowds on the field have left their mark.
The club said the lawn was over and no longer playable.
In Cologne, too, numerous spectators ran onto the pitch after the final whistle to celebrate their team and secure souvenirs, for example in the form of pieces of pitch.
The club stated that many safety precautions had been taken and that fans had also been appealed not to storm the interior.
Additional fences had been put up and the visitors were to be kept away from it with announcements.
There were no injuries in the stadium.