A man was left with a head injury after an altercation between two groups escalated in Station Road, Burgess Hill, in the early hours of Friday morning (5 July).
The incident happened just after midnight outside KB Kebabs.
The two groups had been arguing with each other but then the victim was pushed to the ground where he hit his head.
He needed hospital treatement but has since been released.
A police spokesperson said: “We are anxious to hear from anyone who witnessed what happened just after midnight last Friday. The victim suffered a nasty injury to his head as a result of this incident and it’s important that people come forward with information to enable us to find those responsible.
“Anyone who can assist us with our enquiries is asked to call police on 101 quoting serial 0018 of 5 July. Alternatively call the independent charity Crimestoppers anonymously on 0800 555111.”