Police said in a statement they were still investigating what sparked the Monday night melee between the two performing families, which were both camped on the eastern fringe of the Bavarian city.
Neighbours reported hearing shots during what seemed to be a mass brawl. Police arrived to find a 48-year-old with a bullet wound in his left leg and another five people between the ages of 17 and 55 with minor to moderate injuries.
Each of the families had three members who were suffering injuries. Authorities seized three guns, several knives and batons as well as banned implements such as knuckledusters.
"It is still a complete mystery what led to the massive run-in between the two families from the circus scene," the Oberpfalz police said in a statement.
A police spokesman told the Süddeutsche Zeitung newspaper that the second family had gone to the camp site of the first, seeking “a clarifying conversation.”
The fight may have been about who had the first right to perform, he said. The second circus group, which was newer to Regensburg, had already advertised performances.