Premiership-winning rugby league coach Warren Ryan has been found guilty of assaulting an elderly drinking companion.

Edward Purcell told Waverley Court that Ryan and his brother Chris Ryan were talking about Donald Trump at the Pagewood Hotel in 2016.

"(They were) asking me questions about bloody politics and other things, things I couldn't care less about," Mr Purcell said.

"Eventually Warren said to me 'you're the dumbest so and so I’ve ever met', I said 'maybe I feel the same about you'."

The incident took place at the Pagewood Hotel in 2016. (9NEWS) (9NEWS)

Warren Ryan has been found guilty of assault. (9NEWS) (9NEWS)

He said the former first grade rugby league player then stood up and came "roaring at me like a bull and said 'you mongrel'."

"He came around the table and bang'," Mr Purcell said.

"I just heard a hell of a crack, like a hammer hitting a nail.”

CCTV shows Ryan punch Mr Purcell twice, and a third time when the victim fell to the ground.

Ryan holds his leg up as Mr Purcell tries to kick free, then kicks him in the back.

Ryan told the court the attack was in self-defence.

CCTV shows Ryan punch Mr Purcell twice, and a third time when the victim fell to the ground. (9NEWS) (9NEWS)

He said they were actually discussing penalty rates and "he couldn't muster a decent argument so he got personal. He said I was overbearing."

"I said if you can't understand what I'm saying, you're a bloody moron," Ryan said.

The now-76-year-old said he stood up to go to the bathroom in an attempt to diffuse the situation.

"When I got up to go he said, I'll sort you out," Ryan said.

"First of all I noticed he planted his feet … his left hand was clenched in a fist and I thought 'it's on here now'."

Chris Ryan told the court it was a situation his brother found himself in from time to time because of his public persona.

"They usually have a bee in their bonnet and they become somewhat aggressive or annoying," he said.

While the magistrate agreed he believed there was a threat, he found Ryan's response was excessive, referring to the third punch.

He found Ryan guilty of assault occasioning actual bodily harm on that basis and handed him a 12-month good behaviour bond.