Wiltshire Police has launched an appeal for information after an 18-year-old was punched to the floor in a vicious attack.
The unprovoked assault took place on Fleet Street in Swindon town centre, just after 2.15am on Sunday 3 March.
Released CCTV footage of the incident shows the teenager walking with a friend towards Bushwackers nightclub.
He has his back turned to his attacker, who runs up and punches him once in the back of his head, sending him straight to the floor, face first.
The punch is performed with such force the assailant is almost forced to the ground himself.
The attacker, wearing a dark top, then walks off after the incident, leaving the victim's friend, and concerned passers-by to try and care for him.
The force of the punch saw the victim sustain serious facial injuries including a broken nose, cuts to the face and loss of teeth.
In a statement, Wiltshire Police said: 'The victim was completely unaware of what was about to happen.
The offender ran up behind the victim and, with one very forceful punch, knocked him to the ground.
'This victim did not stand a chance. I believe that he was unconscious before he hit the ground face first.'