Green street hoolsigans attacked green sea urchins in Adelaide’s south-west on Sunday, causing them to flee into the water.
A number of people, including one man, were injured and taken to hospital, including the victim of a serious head injury.
Police are still investigating the incident and the incident is not considered suspicious.
A spokesman for the Australian Red Cross said they were “urgently trying to locate the green street thug” but were not able to confirm his identity.
“We’re asking people who have been involved in the incident to come forward to help police find him,” he said.
“Our thoughts are with the victim and his family at this time.”