A teenage boy stamped on the head of a man for trying to break up a fight, leaving him brain damaged.
The 17-year-old, who has been put behind bars for more than three years, attacked Gordon Friel in Paisley, Renfrewshire, last September.
Mr Friel, 40, was set upon after he tried to act as a peacemaker when two teenagers began arguing.
The court heard how the victim suffered a string of injuries including bleeding on the brain as a result of the assault.
Mr Friel was half his body weight when he was released from hospital following the attack and needed a walking aid.
The attacker, who cannot be named for legal reasons, was sentenced at the High Court in Glasgow on Tuesday.
He had earlier pleaded guilty to assaulting Mr Friel to his severe injury and to the danger of his life.
Judge Sean Murphy QC sentenced him to three years and four months.
The judge told the teenager: "This can only be described as a savage assault."
Two girls - aged 17 and 16 - had also admitted a charge of assaulting the tannery worker.
The elder of the duo - both of whom cannot be identified - was ordered to carry out 150 hours of unpaid work.
The other girl will have to do 100 hours.
The court earlier heard how Mr Friel had been standing on High Street in Paisley eating a takeaway when two youngsters started rowing.
He approached and told the bigger of the two the smaller one did not want a fight.
Prosecutor David Taylor said: "At this point the 17-year-old girl became involved, dragging Gordon to the ground and punching and kicking him on the body.
"She was joined by the 16-year-old girl who shouted 'get him' and began punching him."
He managed to get away before the 17 year-old boy arrived, who wrongly thought Mr Friel had attacked the elder girl.
The boy and others then chased Mr Friel to nearby Forbes Place in the town.
The 17-year-old and others went on to stamp on the victim's head.
Mr Taylor added: "Some members of the pack who had chased were seen to be upset by the ferocity of the assault and a number went to his (Gordon's) aid afterwards - including the 16-year-old girl."
The court heard there was a "footwear mark" on the stricken man's head.
He suffered bleeding in the brain, a liver injury as well as rib fractures. Gordon went on to require three operations.
Mr Taylor said: "Before the incident Mr Friel weighed around 11 stone. On his discharge from hospital his weight was five and a half stones.
"He was so weak he had to use a Zimmer frame to aid walking."
The court was told Mr Friel is now back at work and is expected to make a full recovery although he has no memory of the ordeal.
The 17 year-old boy's lawyer Billy Lavelle said the teenager was now "ashamed of his actions".