Prosecutor Richard Gibbs said that 18-year-old Tai Clark had gone to the Oddfellows pub on November 9 last year to collect his girlfriend, who had gone there with her cousin.
There was an altercation in the pub, which continued in the street after Mr Clark left; and Hardy stepped in between him and a young woman who was acting aggressively towards him.
Mr Clark walked away, but the girl followed, and Hardy again stood between them and asked her: “What do you want to get to happen?”
She responded: “Him to get punched or battered.”
Mr Gibbs said: “Tai Clark has scant recollection, but the next thing he knew, he was on the ground being tended to by the police and an ambulance crew.”
But CCTV coverage showed that Hardy had turned and pushed him to the face, causing him to fall backwards and hit his head.
Mr Clark, whose head was bleeding, had a 1.5cm contusion to the left parietal lobe of his brain and a haematoma to the right of his brain, and Mr Gibbs said the prognosis was unclear.
As a result of the injuries to his brain, he has suffered memory loss and has no sense of taste or smell and a degree of deafness in his left ear – and by the time of the trial in August had still not been able to return to his college course.
Hardy had remained in the area, and when he was arrested nearby he denied culpability, saying he had simply been trying to break up a confrontation.
He entered his plea on the basis that he had intervened to act as peacemaker, but had reacted to a push from Mr Clark.
Mr Gibbs said Hardy had a number of convictions including battery in 2008 and 2012, and wounding with intent using a bottle in 2010 for which he had been jailed for three-and-a-half years.
Paul O’Keefe, defending, said: “He was not out for any trouble. When he left the pub he saw there was a disturbance between Mr Clark and a female who was acting aggressively, and he got between them and broke it up.
“Mr Clark thanks him for his assistance and walks off, followed by the female who is shouting and aggressive.
“Mr Hardy follows and gets between them, and he’s walking backwards telling the female to leave Mr Clark alone.
“At some point while he’s walking backwards Mr Clark is also shouting at the girl, and Mr Hardy walks back into him; and he turns round and pushes very hard into Mr Clark’s face.”
Mr O’Keefe said it had been an impulsive act, and as soon as making contact Hardy turned and began to walk away.
But he then looked back and saw Mr Clark on the floor, so told someone to call an ambulance and remained nearby waiting for the police.
He told officers he could tell them what happened, and he expressed concern for Mr Clark and was apologetic.
Asking the judge to pass a suspended sentence, Mr O’Keefe added that Hardy has a responsible job as a warehouseman.
But jailing Hardy, Recorder David Crigman QC told him: “You were walking backwards seeking to calm and aggressive female.
“There was some contact between your back and Mr Clark, at which your reaction was to turn and push him, and your hand was pushed into his face with such force that he was pushed to the ground and his head hit the ground.
“These courts sometimes have to deal with cases of death where there is one blow and the head then hits the pavement.
“You did not intend those injuries to be caused, but it was your act which led to the chain of events which resulted in them being caused.
“You show a propensity to be quick to violence, and that is what happened on this occasion. I’m quite satisfied the offence is so serious that only a custodial sentence can be justified.”