FREMANTLE player Michael Johnson has been found guilty of assault and fined after punching a man in a late night, drunken kebab shop confrontation in Perth but has avoided a criminal conviction.

The 33-year-old veteran Docker punched schoolteacher Tim Bowen in the face, after Johnson's intoxicated wife Dayna stole Mr Bowen's phone when she saw him filming her husband.

CCTV footage played at Johnson's trial last month in Perth Magistrates Court showed him briefly dropping his pants to his ankles in the kebab shop in Leederville.

Both he and his wife were drunk after attending teammate Jonathon Griffin's wedding on the night of November 12 last year and continued partying in the Leederville entertainment area.

Mr Bowen was sitting nearby with friends in the kebab shop about 3.40am and filmed Johnson on his phone.

Dayna then approaches the group and is seen yelling and apparently abusing them for more than seven minutes on the video footage before snatching Mr Bowen's phone and walking out.

He followed her, sparking the incident with Johnson who punched Mr Bowen, knocking him to the ground motionless and hit his friend Petar Mitanoski before throwing the phone across the street.

Johnson had pleaded not guilty, arguing it was self-defence because a punch was thrown at him and he was protecting his wife who he saw "being pushed, harassed and assaulted".

However, there was no evidence of that on the video, which shows Mr Bowen falling to the ground and an angry Johnson wildly gesturing and waving his arms.

Magistrate Elaine Campione told him it was a "complete overreaction to the situation".

"Clearly Mr Bowen was a much smaller man and vulnerable ... it was a significant blow you delivered, sufficient that he was motionless and had to be assisted up," she said.

However, he was not seriously hurt.

Ms Campione accepted Johnson's lawyer Richard Utting's argument that he should not be convicted because his actions were out of character and he was a well-regarded leader among young indigenous people with references supporting that and pointing to his work with children.

She said if a conviction affected his ability to pass a Working with Children Check "that would be a disaster", given his work in the indigenous community.

Johnson apologised outside court "for my behaviour, especially to the victim".

Fremantle CEO Steve Rosich said any decision on whether a club sanction would be imposed on Johnson would follow further discussions with the board, player and his management.

Ms Campione fined Johnson $3500 plus $188 in costs, $1000 of which will go to Mr Bowen, but granted him a spent conviction allowing him to avoid a criminal record.