A thug reportedly filmed his victim in agony with a broken skull after thumping him repeatedly with a hammer in East Grinstead.
Police have created a computer generated e-fit of the suspect who is alleged to be responsible.
An 18-year-old victim reported being approached on playing fields near Imberhorne School at 1pm on Thursday, June 7.
He suffered a fractured skull and had to be taken to hospital, and police believe he was targeted.
Detective Constable Stuart Beckett said the skinny suspect is aged between 18 and 20, 5ft 10ins, with light brown hair worn in a top knot with shaved sides.
He had unkempt facial stubble, dirty hands and nails with callouses and was carrying a black shoulder bag with red piping and black straps.
Det Con Beckett said: “Following the attack the suspect brazenly used a mobile phone to video-record the injuries inflicted.”
He urges anyone who saw what happened, or who recognises the suspect, to contact the police.
Anyone with information can call 101 and quote serial 663 of 07/06.
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