The assault happened after a ticket inspection on a Zurich bus on Sunday July 1st got seriously out of hand. Six people had to be treated by doctors after the incident.
It all started when a 45-year-old inspector with the city's VBZ transport authority and four of his colleagues were checking tickets on a number 46 bus.
After one passenger was found to be without a ticket, the passenger and the five VBZ staff members got off the bus at a stop near Wipkingen train station.
A photo showing the passenger's back after the alleged assault from the Blick newspaper Twitter account.
A brawl then broke out involving the transport authority staff, the 20-year-old passenger and a 50-year-old passer-by who filmed the incident.
The 45-year-old ticket inspector and the passenger were subsequently arrested. But while the passenger was released later the same day, the ticket inspector remains in investigative custody.
He could remain there for a month as prosecutors investigate possible charges of causing serious bodily harm or attempting to cause serious bodily harm.
Speaking to Swiss tabloid Blick, the Egyptian passenger involved in the incident said he had informed the ticket inspector his travel card had expired and that he should be given a fine.
He said that because he had been in a hurry he had tried to grab the fine notice while it was being written up. But the ticket inspector allegedly responded by taking down his details in a deliberately slow manner.
The passenger then told the VBZ worker he should stop taking himself so seriously because he was "just a fucking ticket inspector”.
The ticket inspector then grabbed the 20-year-old by the collar and pushed him. At that point, the passenger punched back in what he called “self-defence”.
The other VBZ workers then joined the fray. During the brawl, the 45-year-old kicked the bus passenger in the head. His foot is thought to have made contact with the temples, the jaw, an ear and the back of the younger man's head.
A medical examiner later said there was evidence of internal bleeding.
It was this kick that has landed the ticket inspector in investigative custody, according to the Tages Anzeiger newspaper.
A spokesperson for the VBZ later said the incident was highly regrettable. She said she knew of no other similar incidents although personnel with the transit authority checked the tickets of around one million people a day.
She added that the overall incidence of insults and assaults against transport authority workers was down and that staff were given extensive training in how to deescalate tense situations.