The 63-year-old was walking near Pelister Place in Sunshine West when he was set upon by the group of thugs who stole his phone and shoes.
He was dragged onto an oval and stomped on by two 16-year-old gang members.
Deputy Commissioner Rick Nugent spoke about the attack to media.
“I feel sick when I see that type of offending,” he said.
At 1.50pm the grandfather was repeatedly kicked by the younger attackers.
“Just a vicious attack on a person that’s going about their business,” Deputy Commissioner Nugent said.
Three other people were attacked that day, including a university student who was punched in the face and pushed to the ground and had his laptop stolen.
Police say all victims were vulnerable as they were targeted while in a public place waiting to catch public transport.
A 16-year-old boy has been convicted over the assault of the grandfather and slapped with a youth attendance order, meaning he must not reoffend and attend a youth justice unit.
Another 16-year-old boy was sentenced to six months jail, but with time served was released in January.
20-year-old Ramzy Mohammedali was sentenced to eight months in prison, and 18-year-old Amanniwal Nyieker was jailed for two years.
He tried to appeal the sentence and failed.
Victims of Crime Commissioner Fiona McCormack said combating violent offending needed to be a priority.
“Such serious violent crimes … that needs to be taken really seriously by the system,” she said.
In October, police launched Operation Alliance in a bid to crackdown on youth street gangs.
Since then they’ve made 654 arrests, but only 193 were remanded in custody.
More than 80 homes have been searched.