Giving evidence during a judge-alone trial at Manukau District Court today, the complainant said her rugby-star husband was speaking at Otahuhu College on the day in question and she had gone to get a drink to kill time.
While letting a bus a merge in front of her, Mrs Faumuina said the driver behind became impatient and repeatedly tooted their horn.
"I put my hand out and did the middle finger and it just started from there," she said.
Mrs Faumuina cried as she told the court her son Riley, who was one at the time, had been seated in the back of the car.
She pulled over and said the duo came to a stop beside her, yelling that she was "messing with the wrong people".
Mrs Faumuina told Judge John Bergseng she approached their vehicle to explain the incident with the bus and apologised for the one-fingered gesture.
"Get back to that car before I punch the baby out of your stomach," Moka allegedly said.
The heavily-pregnant woman became fearful, she said, when the man made kicking motions to the side of her car where her son was sleeping.
"From then on I was in tears. I just needed to get away from them," Mrs Faumuina said.
She accelerated away and told the court she clipped their wing mirror as she left.
"I wanted to call for help but I knew if I stopped not far from where they were they'd probably carry out the threats they were giving," she said.
Eventually she pulled over again outside a shop but Mrs Faumuina said she spotted the other car approaching at speed, eventually bumping into the side of hers.
"They both came running to the car and the father was just yelling 'you're going to pay. We're gang related'. He grabbed my head with his left hand and punched me right in my forehead," she said.
Kahui also hit her stomach while grabbing for the car keys, she told the court, but the ignition was operated by a button.
Moka's lawyer Esma Brown said the reported threats were fabricated but Mrs Faumuina maintained they were "very true".
"You could've just driven off, right?" Ms Brown asked.
"I could've but I would've just been a mess," she said. "I wanted to just breathe."
Ms Brown said her client accepted he had punched Mrs Faumuina but that it was done legally in the course of citizen's arrest.
"I put it to you he was upset at the time and as he said to you, you'd just run over his daughter and he didn't want you absconding," she said.
Mrs Faumuina denied trying to leave the scene.
Meanwhile, Kahui - who is representing herself - suggested there was a lot of anger coming from the complainant.
She claimed she was run over and had the tyre marks on her legs "to this day" to prove it.
The trial is scheduled to conclude tomorrow.
Mr Faumuina, a bullocking 125kg All Black forward, is understood to have arrived on the scene after police and he will not be called as a witness.
Both defendants are likely to give evidence.
