First-aider Mark Bray narrowly escaped jail because he tended to his victim after punching him to the ground.
University student Ben Gascoigne suffered a fractured skull in the one-punch assault in the early hours of Christmas Day.
Bray, aged 28, had tried to act as a peacemaker when a scuffle erupted outside the Gypsy Queen pub on Drake House Lane, Beighton.
He is a qualified emergency first-aid responder and claimed he acted in self-defence before checking that Mr Gascoigne was breathing.
Bray, of Robin Lane, Beighton, admitted unlawful wounding.
Prosecutor Louise Gallagher told Sheffield Crown Court police found Mr Gascoigne, 21, unconscious outside the pub at 12.45am.
He was taken to hospital with a fractured skull and bleeding on the brain but could remember little about the incident.
His girlfriend said a group of men were fighting in the car park as they left and Bray became aggressive to one of her friends.
Mr Gascoigne tried to separate the two men but Bray struck out and her boyfriend fell to the ground and Bray then tried to help him.
Bray told police: “It was self-defence. I did swing at him but then I checked he was all right.”
He later said he was on his way home when he tried to stop an argument and punches were thrown at him.
The victim has temporarily had to give up his second-year studies and a part-time job at a Meadowhall mobile phone store and suffers with a hearing problem.
He is still receiving treatment at a head injuries centre for loss of memory and impaired cognitive function and has had to stop driving.
Abigail Langford, for part-time loft insulation worker Bray, said: “He is a likeable, hardworking, intelligent young man who has a bright future ahead of him.
“He attempted to help the complainant after the blow. It is clear this defendant was not initially involved in the altercation outside the pub. It was not pre-meditated but extremely foolish.”
Recorder Graeme Cook told Bray: “You went out with the intention of having a good time as did Mr Gascoigne. Your paths crossed in the early hours and I am sure you are thoroughly ashamed of what you have caused with your one punch.”
He said the victim was suffering ongoing effects but Bray was of previous good character and had sought to help the victim. “I accept your version that you were acting as peacemaker,” he said.
Bray was given a 16-month jail term suspended for two years, ordered to carry out 200 hours of unpaid work and he will have to pay the victim £2,000 compensation.