A 75-year-old man suffered a fractured eye socket after a serious assault in Littlehampton, according to Sussex Police.
Police, who are appealing for witnesses, said officers were called to Maltravers Road on the afternoon of Thursday, December 19 to reports a 75-year-old man had been assaulted.
A spokesperson said: "The victim reported being punched in the face four times, and has suffered a fractured eye socket.
"It is believed the assault followed a road rage incident on the roundabout that joins Fitzalan Road and Maltravers Road, between the drivers of a red Hyundai car and a Yamaha 125cc motorbike.
"An 18-year-old man from Arundel has been arrested on suspicion of assault, driving a vehicle without insurance and driving a vehicle otherwise than in accordance with a licence. He has been released under investigation while enquiries continue."
Anyone who saw what happened or who noticed either vehicle being driven shortly beforehand, or who may have relevant dash-cam footage, is asked to contact Sussex Police online or by phoning 101, quoting 605 of 19/12.