The father of Down syndrome baby Leo Forrest allegedly punched and threw a table at a trustee he asked to help look after a fund of hundreds of thousands of dollars raised in a public campaign for his son.

Samuel Forrest, 37, is accused of assaulting Trina McLachlan on July 8 at the rented Massey home he shares with his Armenian wife, Ruzan Badalyan, and son Leo.

Ms McLachlan acted as spokeswoman for him after an online appeal raised more than $500,000 for the baby from 17,900 donors.

Today she told Waitakere District Court how she came to Auckland from the South Island after Forrest invited her to be a trustee on the Leo Forrest Trust.

Tensions were stretched when the pair had a meeting with a bank manager in town.

Forrest wanted full access to the cash but a bank manager suggested making them joint signatories to protect the trust's interests.

When they returned to the defendant's house for dinner events allegedly escalated.

Forrest cooked on the barbecue outside while Ms McLachlan spoke to Ms Badalyan. She said he regularly popped inside to get beers out of the fridge.

When the meal was ready he left them to eat and when he returned he approached the complainant.

"He was in front of me and picked me up and put me over his shoulder. I said 'put me down, put me down'. He dropped me backwards and I landed on my head," Ms McLachlan said.

She requested an apology but instead Forrest went to his bedroom.

"I felt I needed to leave because I didn't feel safe," she said.

Forrest re-emerged with one of Ms McLachlan's bags and allegedly told her to "get out of my house", before throwing some money at her.

Then, she said, he attacked again.

"Sam got the dining table and flipped it at me. The plates went everywhere. It hit me across the chest and ribs," she said. "I didn't say anything. I was just standing in shock and crying.

"I tried to get the suitcase off him and he punched me in the left side of the face."

McLachlan, who gave evidence through tears, said the alleged attack could have been worse if it had not been for Ms Badalyan.

"When Sam threw the table at me, she tried to pull him away. When he punched me she stepped in to stop him doing it again," Ms McLachlan said.

"She was my saviour on the day to be honest."

The pair sat on the couch and the complainant said Forrest threatened his wife not to interfere.

He allegedly told her he could get her deported to Armenia and she would not see their son or any of the money.

Emergency services eventually arrived and Ms McLachlan said the impact of the incident had a severe impact.

She developed a stutter over the following three months, balance problems and blurred vision, she told the court.

"I blame myself for freezing on the night because I should've protected myself," Ms McLachlan said.

"It's made me not be the person I am."

If found guilty, Forrest faces up to two years in jail.

The judge-alone trial is set to finish this afternoon.