The man, who was 25 at the time, had experienced ongoing pain and numbness.
He had been forced to live on mashed food for three months and was still unable to fully open his mouth.
He had been part of a group in Blackmore Cres, Alexandra, walking to a friend's house on May 28 last year, when they were approached by Robinson and Hammond.
After throwing cans at the group, Robinson began the assault.
Crown prosecutor Richard Smith called the ensuing onslaught "persistent, prolonged and gratuitous".
Once Hammond joined his friend swinging punches, it was not long before the victim fell down.
"He was defenceless from the moment he hit the ground but that didn't deter you," Judge Michael Turner said.
The pair continued to rain down blows on the vulnerable man until the screams of his friends persuaded them to stop.
"What did you two do? Did you help? No.
"He was bleeding profusely. Did you assist? No," said the judge.
The victim, unable to walk without assistance, was helped to an address 300m away and the defendants followed.
As the bloodied man was tended to in the kitchen, Robinson, uninvited, entered the home.
"It appeared to the victim's associates that the defendants were intent on entering the dwelling to continue assaulting the victim," the police summary said.
However, Robinson was repelled by two people and physically removed from the property.
"This really is thuggery, plain and simple," Smith, said.
When it came to explanations for the sustained violence, the defendants offered up a variety of excuses.
Hammond said the victim's group had been yelling gang slogans and had been "looking for a fight".
He had a hand injury at the time, so his punches would not have landed with such force, Hammond claimed.
It had been purely coincidental that he had ended up at the same house as the victim, Robinson said.
He had not been following the victim.
Judge Turner called their claims minimisation and suggested they contained elements of "victim-blaming".
The victim, he noted, had suffered psychologically since the attack.
He reported feelings of anxiety, had become reclusive and his memory had been adversely affected as a result of the head injury.
He had been just about to start a new job, which had since fallen through.
He had been pursued by creditors as a result of the resulting financial hardship.
He was forced to move out of his flat.
As well as the injuring charge, Robinson was convicted on two breaches of community work, a sentence he received in 2019 for domestic violence.
