Police are appealing for witnesses following an assault in the alleyway between Daniaud Court and Halse Road in Brackley which took place between 9pm and 9.15pm yesterday (Thursday).
The victim, a 16-year-old boy, was approached from behind, jumped on and punched.
Three offenders ran off when the victim got up to defend himself.
They are described as white, about 16-years-old, 6ft tall and of slim build.
Anyone with information, should call Northamptonshire Police on 101 or Crimestoppers on 0800 555 111.