The cyclist accused of killing Hove greengrocer Tony Magdi faces prison after he admitted manslaughter at a hearing at Hove Crown Court.
Paul Lambeth, 36, of Stafford Road, Brighton, attacked Mr Magdi in Portland Road, Hove, last November.
Mr Magdi, 52, who lived and worked in Portland Road, had opened the door of his car as three cyclists rode past, including Lambeth, causing them to swerve.
The popular greengrocer suffered serious head injuries in the attack on Sunday 7 November when he was knocked down by a single punch.
He is believed to have suffered the critical injury when he fell and spent the next three weeks in a coma in hospital in Haywards Heath where he died.
Lambeth also faced a charge of having cannabis but this has been dropped.
He was remanded on bail until Friday 3 June when he is due to be sentenced at Lewes Crown Court.