Man knocked out in Rotterdam brawl

Images are circulating on social networks showing a brawl in front of De Doelen in Rotterdam. A man can be seen hitting another person with a violent blow, leaving the latter motionless on the ground. Immediately afterwards, a third person picks up a traffic sign lying on the ground and in turn hits the man who had just knocked out the other. The reason for the argument is not yet known. The video is widely circulated and draws attention to this street incident.