The incident happened in Coalpool Lane, Walsall, at about 9pm on Sunday is believed to have involved a group of teenage boys and girls.
The bus had stopped for a passenger to get off when the group standing outside managed to turn the engine off from the back of the vehicle.
The driver got out to confront the youths and was attacked, before a brick was thrown through the window.
An engineer's van was also damaged.
A spokesman for West Midlands Police said: "We’re investigating after a bus driver was attacked on Coalpool Lane in Walsall, at around 9pm last night.
"He had stopped the bus to let a passenger off, when a group of people standing on the road managed to deliberately turn the engine off from the rear of the bus.
"They then assaulted the bus driver when he went to confront them.
"The same group then threw a brick through the window of the bus and also caused damage to an engineer’s van.
"Enquiries continue and anyone with information is asked to contact us via Live Chat at west-midlands.police.uk between 8am and midnight, or call 101 anytime.
"Crimestoppers can be called anonymously on 0800 555 111. Please quote crime reference 20WS/261316P/20."