Nepean Little Athletics president John Galea, 42, approached spectators who were standing in a restricted area during a meeting at Blair Oval, in St Marys, about 7.40pm on Friday.

An argument ensued when he asked a group of parents to move from the sports field and one of the men punched Mr Galea on the head. He was treated at the scene, then taken to Nepean Hospital suffering from concussion.

The other men fled the scene.

The chief executive of Little Athletics NSW, Kerry O'Keefe, said it was the first time in its history that such an incident had occurred.

''It is something that we do not tolerate and it is deplorable,'' Ms O'Keefe said. ''The association does not tolerate any form of abuse and will fully investigate the matter.''

She said she had spoken to Mr Galea and he was ''fine''. He was released from hospital on Friday.

When contacted by The Sun-Herald on Saturday, Mr Galea said: ''I have been asked not to make comments.''

More than 40,000 children aged between five and 16 are registered at 200 Little Athletics centres across the state. Hundreds were at the meeting when the fight broke out, Ms O'Keefe said.

Parents yesterday expressed concern that such violence could occur at a children's sporting event.

Nola Boelhouwer, the mother of 14-year-old Nepean Little Athletics co-club captain Adrian, said she learnt of the incident through her father who was at the event. ''It was a bit of a shock,'' she said. ''As far as I know, legally, no parents are allowed on the oval and [Mr Galea] has probably asked one of them to get off the oval.''

Tony Coppini, of Colyton, said his daughter Victoria, the club's other co-captain, had been on the track competing in her long-distance running event when the altercation occurred. ''She didn't see anything, she was up near the railway end,'' he said. ''I was up the other end [of the stadium]. I heard he got hit.''

The incident is the latest in a string of fights to have broken out at junior sporting events this year.

In July, Gary Harling was knocked unconscious in a brawl involving four men at an under-12s junior rugby league game at the Glenwood oval.

Two men, including Mr Harling, were later charged with assault occasioning actual bodily harm.