Boy, 15, left unconscious in attack in Rottingdean
A 15-year-old boy was knocked down an embankment and left unconscious during an attack by a masked man.
Sussex Police said the man ran towards the teenager and struck him in the face in Court Ord Road, Rottingdean, near Brighton, at about 1600 BST on Tuesday.
The force of the blow caused the boy to fall down an embankment and hit his head on a tree, which knocked him out.
He was found two hours later by a member of the public. Officers have carried out house-to-house inquiries.
Det Con Tracey Dixon said: "The unprovoked assault left the victim in a potentially serious and vulnerable condition.
"PCSOs have been supporting the investigation team in conducting house-to-house inquiries and we are now following a number of lines of inquiry.
"Police have spoken to local residents and the man has been seen in the area in the last six months.
"If anyone has seen this man or has any information about this assault they should contact us immediately."
The suspect was described as being in his early 20s, of medium build and 6ft 2in tall.
He was wearing a black balaclava and camouflage trousers.