Nova Whiting-Willett, 36 alleges that Wayne McCatty, a 34-year-old dad, slammed her head into the floor of the vehicle in view of her terrified three-year-old daughter and two children he was travelling with.
Ms Whiting-Willett claims that McCatty punched her after a row broke out when he tried to ram his buggy into a small space beside her.
Ms Whiting-Willett told the jury at Kingston crown court: 'I told him I could not move. He said aggressively, 'You are going to have to f***ing move'.
'I remember being punched and being on the floor. He had hold of my head and was banging it against the floor.'
McCatty admitted he was the man seen on the bus CCTV, but denied assaulting Nova Whiting-Willett, claiming it was self defence. He also denies assaulting her husband, Anders.
Ms Whiting-Willett admitted to the court that she lashed out at McCatty after being hit.
The trial continues.