The father of a sexually assaulted girl who lunged at her abuser in the dock at the High Court in New Plymouth was warned he could be jailed.

The judge's warning came after the man pleaded guilty in New Plymouth District Court yesterday to a charge of assault with a weapon on June 29.

A less serious charge of possession of an offensive weapon (a glass) was withdrawn.

His lawyer, Andrew Laurenson, said his client lost his temper when the prisoner, Grant Selby, who subjected his daughter to sustained sexual abuse, "gave him the fingers" from the dock.

The court heard how the man had leapt out of his seat in the public gallery, grabbed a glass from a lawyer's desk and tried to attack Selby, yelling that he had been "messing with his kids".

He was grabbed by prison officers and ejected from the court.

He later admitted he snapped when Selby gestured at him.

Judge Roberts said he was considering jail because the man's actions brought the whole court process into disrepute.

"The High Court judge took a particularly dim view," Judge Roberts said, as did he.

The man had already been warned to control himself during Selby's earlier appearances before him in the District Court.

Mr Laurenson countered his client had suffered extreme provocation. His client was extremely remorseful and apologetic.

He was thought of very highly by his employers and had in recent years got his life in order.

"He accepts he behaved badly but it was not without extreme provocation from Mr Selby.

"Prison in those circumstances would be extremely harsh."

Judge Roberts convicted the man, calling for a pre-sentence report covering all sentencing options.

"I give no indication he will escape prison," the judge said.

Judge Roberts made an interim order suppressing the man's name. He will be sentenced on September 14.

- © Fairfax NZ News