A High Court judge has labelled a 17-year-old's psychiatric report as "chilling", before jailing him to protect the public from his violent behaviour.

Cory Taipari, known as CJ, was yesterday sentenced in the High Court at Hamilton on a charge of wounding with intent to cause grievous bodily harm after attacking a man with a samurai sword near Thames in January 2013.

Justice Graham Lang sentenced Taipari to six years and nine months in prison. It was in addition to a four-year, six-month sentence he was already serving for similar offending in August 2012. It would ensure Taipari spends up to about 11 years in jail.

Compounding Taipari's sentence was that he was also yesterday ordered by Justice Lang to serve a minimum term of imprisonment, primarily to protect the public, of four years and six months on his latest charge.

Taipari was on bail and just two weeks out from a defended hearing for the first incident - for which he was later convicted on a charge of wounding with intent to cause grievous bodily harm - when he attacked a man with the samurai sword at a Matatoki property on January 28, 2013.

It caused a 2cm deep gash on the man's neck, just 1mm away from causing a fatal injury.

The attack left the 23-year-old victim with permanent nerve damage on the side of the face, as the weapon became embedded in the man's neck, just behind his ear.

In determining whether to impose a minimum term of imprisonment, Justice Lang had to take into account the protection of the public.

He read an excerpt from Taipari's psychiatric report which noted he would need "intensive" rehabilitation to change entrenched violent and self-harming behaviours brought about by his upbringing.

"This report makes chilling reading because it points out the depravations and neglect that you have suffered through your youth.

"You are the product of a very poor home environment where both parents were neglectful in the extreme and engaged in substance and alcohol abuse," the judge said.

"You have limited educational opportunities because you were expelled from school at an early age because of your disruptive behaviour."

In confirming the minimum prison term, Justice Lang said the matters identified in that report showed "that you are at a very high risk of violently reoffending on your release into the community".

Taipari's lawyer Mike McIvor said any jail term, especially one with a minimum term, would be "crushing" for his client.

McIvor said the sword had a broken handle and was "wobbling around" as he chased the victim, and didn't mean for it touch his head.

Taipari's family, who were in court to support him, declined to comment when approached by the Waikato Times.

Cory Taipari's brother, AJ Taipari, 22, yesterday withdrew his guilty plea to a charge of wounding with intent in connection with the Thames attack. He will reappear in court at a later date.