A lower-grade rugby union player in the Canberra competition has allegedly headbutted a referee and king-hit an opponent.

The ugly incident, to which police were called, took place during the fourth-grade match between Wests and Queanbeyan at Campese Oval on Saturday.

The trouble began when the Wests player was shown a yellow card by the referee for repeated infringements.

The Wests player is then alleged to have headbutted the referee in the chest and wiped blood from a head cut on him.

After then receiving a red card and being asked to leave the field, the Wests player allegedly hit Queanbeyan player Adam Res when Res wasn't looking.

The Wests player also is alleged to have punched Queanbeyan captain-coach Grant Jones, who had come to his player's defence.

A police spokesman confirmed they were investigating an alleged assault on a 20-year-old Queanbeyan man.

"In a game such as rugby, there's an implied level of [consent] to physical contact however we're investigating to determine whether this incident has gone beyond that," the spokesman said. 

He said police are still following up with witnesses, and have not laid any charges. 

An official from Wests said the club would not comment as the matter was under police investigation. He refused to reveal the identity of the Wests player involved.

However, the official said there were "five or six different versions of events".

It was his understanding that the Wests player was dazed and fell forward into the referee, rather than headbutt him as alleged by others.

One of those watching was Queanbeyan second-grade coach Nick McCarthy, who posted a message on Facebook on Saturday night condemning what had taken place.

"Today I witnessed the most horrendous thing I’ve ever seen on a football field," McCarthy wrote.

"(A) player (was) yellow-carded for repeated infringements (then) proceeds to headbutt the volunteer referee.

"Then after the referee adds a red card to the scenario the player punches an unsuspecting player.

"The actions on the field were made worse by the reaction of the administration of the offending club defending the player's actions.

"I hope you never ruin our game again and spend time as a guest of the state.

"Also to Wests Rugby Canberra, you should be ashamed that you couldn’t put the game and the law before club rivalries."

The matter is expected to heard at the competition judiciary on Monday or Tuesday night.

A spokesperson from Brumbies Rugby was unavailable for comment.

Queanbeyan went on to win the game 22-14.

With Fleta Page