Nottingham Crown Court heard this week how 22-year-old James House, of Browning Close, Worksop, hit his victim just once in the attack on 19th October last year.
But the blow was strong enough to send Lee Richardson to the floor, hitting his head on the kerb and fracturing his skull.
House originally denied the charge of wounding or inflicting grievous bodily harm. But he changed his plea at the last minute on Tuesday 20th August, the day he was due to stand trial.
Judge Jonathan Teare adjourned the case for psychiatric reports before House is sentenced on 18th October.
He had already told House that if he admitted his guilt he would face a maximum prison sentence of 16 months.
The judge told him: “You have a previous conviction for serious violence.”
But he added: “I am keeping an open mind until I have read the reports on you.”
The court heard that the attack took place near a bookmaker’s shop in Worksop at around 9pm on 19th October 2012.
The victim, Mr Richardson, also 22, had been talking to someone else when House crossed the road and threw one punch at him.
He fell and hit his head on the kerb, causing an audible crack which was heard by witnesses.
Mr Richardson was taken to Bassetlaw Hospital and later transferred to the Royal Hallamshire Hospital neurosurgery department in Sheffield before returning to Bassetlaw on 25th October.
At the time a consultant neurosurgeon gave a statement saying the injury was ‘quite severe’ and that it was difficult to give a long term prognosis.
But the Guardian understands he has since made a good recovery. The prosecution said he was not in intensive care and suffered no brain damage.
The court heard that House committed the offence just days before he was due to finish a community order for another similar assault.
On 24th October 2011 Worksop magistrates sentenced him to a year long order including sessions with an alcohol worker, and four months tagged on a night time curfew.
He had admitted common assault after an ‘unprovoked’ attack in which he repeatedly punched a man to the head, body and face.
Previous to that he had served a two year detention and training sentence for another wounding incident.
At Tuesday’s hearing House’s barrister Sarah Munro asked for psychiatric and probation reports on her client before he is sentenced.
The judge adjourned the case to Friday 18th October.