With an "axe to grind" Lisa Kazazi spun her car around outside the courthouse and confronted Ronald Charles Peacock about a fire at her house.
He then punched her in the nose.
Peacock was convicted by Judge Bruce Davidson of assaulting Ms Kazazi following a defended hearing in Masterton District Court this week.
He claimed she had injured herself.
Peacock represented himself at the hearing. Judge Davidson appointed lawyer Peter Stevens as amicus curiae to help him.
Police prosecutor Sergeant Garry Wilson said there had been an ongoing dispute between the pair resulting in an argument outside the court on February 19 and Peacock punching her.
In evidence, communications technician Setu Solomane said he heard the commotion from inside his car parked outside the courthouse.
He heard a woman screaming and Peacock yelling back at her to 'stay away from me".
Mr Solomane told the court the pair kept arguing and Peacock punched her to the face with his right fist.
"She had blood on her nose," he said.
In evidence, Ms Kazazi said she had known Peacock for five years.
On the morning Peacock hit her, Ms Kazazi said she was driving past the courthouse when she heard Peacock yelling at her so she spun around and parked up.
She confronted him about the fire, when she got hit.
Ms Kazazi said she was "100 per cent sure" Peacock had head butted her not punched her.
She told the court she believed Peacock had burnt her house.
"I was traumatised and stressed. I was distressed ... we have lost everything ... I was asking Ron why he did what he did. He started yelling in my face. It became heated. He was intimidating me ... he then said you want to play the game and he smashed me on the top of the nose ... I was frightened."
In cross examination Peacock put to Ms Kazazi she was set on confronting him but she denied this.
"You are a violent man ... I do believe you burnt down my home ... I was badly traumatised."
Peacock said the victim had yelled "it's not over".
"I kept telling her to stay away."
Judge Davidson said it was clear emotions had been running high between the pair at the time of the assault.
"You both have an axe to grind with each other ... others have been dragged into the circle of dispute."
Mr Solomane was a credible witness, the judge said. "It is clear there was an assault."
He convicted Peacock and ordered he pay $25 in witness expenses and fined him $400.