About six staples were needed to close up the laceration on a Whanganui man's head following an attack in 2013.

Thomas Rainford and two unidentified friends were behind the assault, which also left the victim with a chipped finger bone and "significant bruising", the Whanganui District Court heard.

Rainford was before the court for trial on a charge of wounding with intent to cause grievous bodily harm. The charge was downgraded to wounding with intent to injure later in the day, and Rainford pleaded guilty, ending the trial.

The attack happened after the victim's daughter's housewarming party at a house in Swiss Ave, Gonville, on November 17, 2013.

Advertisement
Advertise with NZME.

Before the charge amendment, a witness gave evidence about the attack.

The witness, who is the victim's daughter's partner, said he went to high school with Rainford some years back.

He said Rainford and two friends showed up at the party, and he went to greet Rainford and shake his hand. However, when he went to introduce himself to one of Rainford's friends and shake his hand, the friend punched him to the ground.

The witness went back inside and a scuffle ensued between the men and other party guests.

The men left shortly after.

But after midnight, when the victim and the witness were sitting outside on a fence, the witness saw the three men approach from across the street, with one of them holding what he thought was a machete behind his back.

"I remember Thomas asking [the victim] if he could have his shoe back," the witness said.

"He said no ... that's when [the victim] got attacked."

He said all three men were striking the victim with weapons around the head and body.

He ran to get help from police officers who were attending a car crash down the road.

Crown prosecutor Harry Mallalieu said the victim was taken to hospital with a cut on his head, which needed about six staples to close.

The victim also needed surgery for the chipped bone on his fingertip, and he suffered significant bruising, Mr Mallalieu said.

After Rainford's guilty plea, Judge David Cameron explained to the jury why the trial had ended so soon.

"When people hear good and direct evidence against them, they often change their position," he said.

He remanded Rainford in custody to March 17 for sentencing.