The son of a high-profile public servant could be too scared to tell the truth after allegedly being punched in the head by his father in downtown Wellington, a court was told today.

The man, whose name and occupation are suppressed, has pleaded not guilty to one charge of assault on a family member over the incident, in Manners Mall in August 2008.

At Wellington District Court today, defence lawyer Mike Antunovic said the man had not punched his son but rather had attempted to remove a bag slung over the boy's shoulder while in the back seat of a parked car.

The boy had bought the bag after running away with $700 he stole from his mother.

Mr Antunovic said the boy had a history of dishonest and troublesome behaviour and the man was trying just trying to look out for his son.

Giving evidence via video link, the boy said he had exaggerated his initial complaint to police and his father had never punched him.

"If there was any contact at all it was all unintentional," he said.

During questioning by crown prosecutor Paul Dacre, the boy said he could not recall why he initially complained to police but he had been upset and scared.

"Everything was happening a bit more seriously than I'd planned out," he said.

"I was scared of what was going to happen, not (of) any particular person."

The boy, diagnosed with attention deficit hyperactivity disorder (ADHD) after making the complaint, said his father had touched him but the contact was "suitable".

Crown witness Melissa Dol, 18, today told the court she saw the man dragging the boy to a car before repeatedly punching him in the head.

Mr Antunovic asked Ms Dol if, in light of the boy's admission, it was possible she had mistaken the struggle for the bag as punches.

"No, I don't think I was mistaken," she said.

"I don't think anyone should drag their child down the street," she said.

"I think that he could be scared to say that (he was punched) in front of his dad."

Cayne Wright, who also witnessed the incident, said he saw the man put the boy in the back of the car and punch him.

Mr Antunovic also questioned Mr Wright's account, saying he could have been mistaken given that he was across the road and looking through the car window.

The trial continues.