Seven police units were called to Exeter High Street after reports of a man armed with either a knife, hammer or piece of wood.
A police spokesman confirmed a man had been pushed off a bicycle in an alleged robbery.
"Two men were involved in an altercation and one man was injured.
"We have been told that one man was being assaulted with some kind of weapon. We have had different reports that there was possibly a knife, a hammer or even a piece of wood.
"The victim ran off towards the Iron Bridge.
"A man aged 20 from Exeter was arrested near the Guidhall entrance and is now in police custody. We have also found the victim and the bicycle."
It followed an earlier incident on Fore Street outside McCoys Arcade when two police units were called to stop and search a green Jaguar.
The car was seized and the driver was charged with having no insurance and no driver's licence.
