It took more than 40 minutes to get him to the hospital in Frankton after medical staff at the tournament allegedly assumed he was very drunk.
The medical process was then drawn out further by four hospital staff who also assumed his state was alcohol-related, they say.
"I lay in Queenstown Hospital with all of them thinking I was drunk, until about 3pm the next day."
It was only when a nurse, who was at the tournament the day before and saw the incident, approached hospital staff that they conceded it was more than just a hangover, and he was sent to Invercargill hospital for a CT scan on his head.
The scan detected bleeding on the brain and 30 minutes later he was flown to Dunedin Hospital where he had another CT scan and neurosurgery.
Mr Cottier remained in a high dependency unit for a further two weeks after the operation and is now waiting radiation therapy.
Mr Cottier has what can be compared to a scab on the brain, which if knocked will start severe and possibly lethal bleeding again.
"I'm a bit annoyed. At the end of the day doctors are doctors and they can't just say 'he's a drunk teen'. They have to assume the worst and they didn't in this case."
Mrs Cottier said after a call from his friend she arrived to the rugby grounds to find four medical staff standing over her son and "retired army paramedic slapping" her son's head and announcing he was drunk.
"It was atrocious, unbelievably bad."
Mrs Cottier wrote a letter a month ago designed to go to the hospital, local MP Bill English and the medical complaints authority.
Southland chief medical officer David Tulloch said a review process of Mr Cottier's case would take place once the complaint was made by the Cottier family.
"We are concerned by the issues raised around Alex Cottier's treatment and would welcome the opportunity to discuss his treatment with Alex and his family."
The board would not comment any further on the specifics of Mr Cottier's treatement.