"I could feel my head smash on the concrete ... it's just scary because I couldn't really remember it," the victim said in the video.
Oram said the suspect then "milled around" either out of concern or just to watch the situation unfold.
The victim's friends tried to intervene to prevent the suspect from leaving and there was an altercation, the sergeant said.
The suspect was then captured by CCTV footage running up Ballarat Mall, along Camp St and down Shotover St.
He is described as a European male, possibly in his early 20s, wearing a black jacket, baggy blue jeans and white Nike shoes.
"I know that family or friends, or even an ex-teacher, will know who he is and we are asking for them to come forward.
"If we don't catch up with this male he is going to go on and cause someone some serious harm," Oram said.
The victim, who was concussed, said he was hesitant to return to town in case a similar situation occurred, and if the police caught the person responsible it would be a relief for him and his family.
* Police: 0800 107-INFO.
-- lucy.wormald@odt.co.nz