"I looked to my right and I saw three guys jump out of a van and they just started punching the passenger front window [of the car in front]," he told the Herald.
"Eventually, that smashed and got glass all over the road. Then they proceeded to punch the passenger.
"It was a red light and there was a car in front of the car that was being punched, so they couldn't get away until the light turned green."
He said the man being attacked appeared to be in his mid-30s.
"It was just screaming from the female driver of the car.
"I think she was just yelling: 'Leave him alone, leave him alone'.''
Hape said the three men had been riding in a dark blue company van belonging to Harbour City Ceilings.
The company was not answering phone calls this morning.
The incident lasted for about 30 seconds, Hape said, before the car drove off - followed by the van.
"The guys just jumped back into the van and then drove off.''
The incident was witnessed by a number of pedestrians, motorists and passengers of at least two buses nearby.
Hape said two men jumped in to stop the attack near the end, while others got on their phones to authorities.
Police have since spoken to one of the men, who will be summoned to appear in court at a later date, a police spokeswoman said.
