New Year's Eve started well for Shaun McNeil, a self-proclaimed mixed martial arts fighter.

Two hours after he and his partner Sonya Walker left her children with a babysitter and hit the town, the 25-year-old labourer was in a reflective mood.

''It's a year to forget to forgive to let go and smile at,'' he posted online at 5pm as he hopped between city bars. ''Move on take on new adventure new life new love and smile''.

But police allege four hours later, with eight beers and one wine under his belt, Mr McNeil punched four men in brutal and unprovoked assaults in Kings Cross, leaving one clinging to life in an intensive care unit.

In the exact spot 18-year-old Thomas Kelly was fatally king-hit in 2012, 18-year-old Daniel Christie was allegedly punched once in the head, causing him to fall to the pavement, fracturing his skull leaving him in a critical condition.

Police allege Mr Christie and his brother Peter, who had just arrived to ring in the new year, were attacked after going to the aid of two teenagers being assaulted by Mr McNeil.

It began with a random verbal altercation on Victoria Road between Mr McNeil and two ''very slightly built'' teenagers, Jack Flynn and Tony Gill, police documents state.

''I'm an MMA [mixed martial arts] fighter,'' Mr McNeil warned the pair before allegedly punching Mr Flynn in the head, causing him to fall to the ground.

Mr Gill went to his mate's aid and was allegedly punched too.

When the pair tried to hide behind Daniel and Peter Christie, who were simply walking past, Mr McNeil shifted his gaze.

''The accused at this time has turned to [Daniel] and immediately became aggressive and stated, ''I'm an MMA fighter,'' police documents state.

Daniel was allegedly punched once to the face, causing him to immediately lose consciousness and hit the ground.

Peter tried to throw himself between Mr McNeil and his brother and was also allegedly punched and left with a cut lip.

Roving police arrested Mr McNeil as Daniel was rushed to St Vincent's Hospital, where one patient was being admitted every 30 minutes after being knocked unconscious on New Year's Eve.

On Wednesday, Michael and Maureen Christie, from Thornleigh, remained at their son's bedside as he clung to life with bleeding on the brain, pressure to the skull and several fractures.

Just weeks after graduating from Pennant Hills High School, the rugby-mad teenager, who was starting a T-shirt design business with his brother, now faces a prognosis of considerable brain injury, police said.

Through a legal aid lawyer, Mr McNeil, from Pennant Hills, told Parramatta Bail Court that Mr Flynn and Mr Gill had initially approached him about purchasing drugs so he had become ''protective'' of his partner.

He told police he was not drunk and believed he was going to be assaulted by the group.

However, police prosecutor Lisa McEvoy painted a picture of a ''very, very violent man'' whose attack was ''completely unprovoked and completely unfair''.

She said Mr McNeil ''doesn't live in a box'' and would have seen media coverage about king hits and alcohol-related violence.

The court registrar agreed and said ''given the current climate'' of media coverage and the ''very strong'' prosecution case, it would be inappropriate to grant bail.

In a blue forensic jumpsuit and with a cut to his lip, Mr McNeil cried as he was remanded in custody.

"He’s very distressed, he’s devastated about what’s happened to the boy and he said it was not unprovoked," his mother Sharen McCormack said.

Mr McNeil was one of 173 people arrested on New Year’s Eve for 222 offences, significantly more than the 97 arrests last year.

"The message is getting through but not to the people who need to hear it most," said Professor Gordian Fulde, director of emergency at St Vincent’s.

"Every hour we had at least two patients who had been knocked unconscious. It’s not just violence, it’s brutality."

with Rachel Browne