An 18-year-old man was taken to hospital after an attack by up to ten young people in Bexhill, according to Sussex Police.
Police are seeking witnesses after the man was attacked and robbed in Sackville Road, Bexhill-on-Sea, at around 10pm on Tuesday, July 23.
A spokesman said: "A man aged 18, was attacked by up to ten other young people before having a black-and-brown bag stolen from him.
"The bag contained his wallet, mobile phone and other personal items.
"The victim sustained head injuries for which he was treated at the Conquest Hospital, St Leonards-on-Sea."
A 21-year-old man has since been arrested on suspicion of robbery, interviewed and released under investigation while enquiries continue, police revealed.
The spokesman added: "Anyone able to assist officers is asked to report details online or phone 101, quoting serial 1690 of 23/07.
"Alternatively they can contact the independent charity Crimestoppers anonymously on 0800 555 111."