The local transport authorities said 11 people were injured when the metrobus — a bus that travels in its own special lane — lost control and ploughed into a line of commuter traffic.
The bus drove over three cars, causing huge damage and the key highway to be shut at the height of the morning rush hour.
Video footage broadcast by Turkish television showed that the accident happened when one of the passengers — who had previously been arguing with the driver — swung at him with an umbrella.
The driver appeared to lunge back, falling out of his seat with the bus careering into the traffic going the other way.
A man aged 35 suspected of being the umbrella-wielding attacker was detained and is now being questioned by police, the official Anadolu news agency said.
The incident is one of the more striking recent examples of the dangers of travelling on Istanbul’s roads, with television frequently reporting outrageous behaviour by drivers and passengers alike.