An amateur boxer was sentenced to life with a minimum term of 16 years after he was convicted of the murder of a father of two with a single punch.

Bradley Hinkler aimed a “devastating” fatal right hook to the side of victim Thomas Gower’s face outside a bar in Sheffield city centre just minutes after knocking out another man.

Hinkler, 20, attacked both Mr Gower and his friend Richard Howard. Both victims were unconscious before they hit the ground, but Mr Howard survived the attack on December 18 last year. Mr Gower, 26, died eight days later in hospital following the assault outside Alibi bar in Sheffield city centre.

Hinkler, of Woodthorpe, Sheffield was found guilty of murdering Mr Gower and assaulting Mr Howard causing grievous bodily harm with intent by a jury at Sheffield Crown Court after a two-week trial.

After yesterday’s hearing Hinkler’s uncle Chris Smedley who trained him as a boxer said the family were considering launching an appeal. He said: “The sentence is absolutely shocking. It should have been a conviction for manslaughter 100 per cent.”

He has previous convictions for two public order offences, possessing a controlled drug and two cautions for battery.

Judge Simon Lawler said his behaviour on the night was “callous beyond belief.” He said of the attack on Mr Gower: “It was a quite unnecessary and cowardly attack on a defenceless man.”

The judge said the impression given to the public by Hinkler’s supporters after the jury’s verdict did not “give the full picture”. It was very different from the “one punch scenario” which results in death and is often charged as manslaughter.

He said: “Extensive, independent eyewitness accounts clearly showed you Bradley Hinkler for some reason or reasons were on that night in a violent, aggressive and ugly mood.” One witness described Hinkler as a “predator going out for another kill”.

The court heard Mr Gower never even saw the punch. “The defendant chased him down and attacked him from the rear in a cowardly way,” said prosecutor Nicholas Clarke QC. Hinkler was a fit and active boxer who trained almost daily at a gym. “Although only a medium build he packs a powerful punch,” said Mr Clarke.

Mr Gower died on Boxing Day in hospital from head injuries after suffering a skull fracture from the fall and a broken jaw caused by the punch.

When arrested Hinkler claimed he was elsewhere, then said he acted in self-defence because Mr Howard was holding a bottle and he believed Mr Gower was going to get a knife. He told the court he was “devastated” by the events and claimed the two men had followed him out of the bar.

Judge Lawler said it was not a case of self-defence and after striking Mr Gower, Hinkler calmly walked away as if nothing had happened.

The judge added: “This was violence on the street witnessed by many totally innocent people enjoying an evening out.”

He praised Mr Gower’s family for acting with dignity throughout the proceedings and said he hoped others with different views on the case would exercise similar restraint.

After the hearing Det Supt Andy Thompson who led the police inquiry said: “Bradley Hinkler was out with friends and was clearly intending to get involved in violence. As an experienced and talented amateur boxer he should have known better.”