A youth team football match had to be abandoned after an adult spectator ran on to the pitch and punched a 13-year-old player in the face.
Police and the Sussex Football Association (SFA) are investigating the incident, which took place during an under-13s County Cup match between Hove Park Colts and Woodingdean Youth on Sunday.
The referee ordered the game to be abandoned after the incident, which happened 20 minutes into the game at Aldrington recreation ground, Hove.
Ken Benham, chief executive of the SFA, said: "We deplore any incident of this kind and are concerned about the dreadful consequences such an action might have on a child of that age.
"The referee has sent in his report and the entire matter is now under investigation.
"The police are also involved, although we have no notice of any charges being brought."
Mr Benham said as far as he was aware nobody had been seriously injured.
He said: "The match had to be abandoned. At this stage, I don't know whether the game will be rescheduled or not.
"It depends on the outcome of the investigation."
He said the inquiry would be completed within a fortnight after witnesses had been spoken to and both clubs had sent in their own reports.
Alan Hatherillo, secretary of Hove Park Colts FC, said: "We have nothing to say. The matter is in the hands of the police."
Vanessa Childs, secretary of Woodingdean Youth FC, also declined to comment.
A spokesman for Hove police said: "We responded to an alleged assault at the recreation ground on Sunday morning.
"It concerned a 13-year-old boy who was allegedly punched in the face.
"The boy subsequently went to Hove police station and was interviewed by officers.
"We are still speaking with the alleged victim and his parents as to how they wish to proceed with this. Until then, we can make no further comment."
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