A teen was sitting at the beach watching the ships out at sea when, in an unprovoked attack, a man struck him around the head with a metal drink bottle, causing him a brain injury.
The 14-year-old was at Bell Block beach, in New Plymouth, seated at a picnic table with his friend when Joshua Cornwall arrived in a car.
Cornwall, 29, got out of the vehicle, approached the teen and demanded his bag, Judge Gregory Hikaka told New Plymouth District Court on Friday.
The teen refused to hand over his property, which led to Cornwall attempting to pull it from him before striking him with a metal drink bottle.
The force of the blow was so severe the teen was knocked unconscious and collapsed to the ground.
Cornwall took the bag, which contained bike tools and around $70, legged it to the car and left the scene.
The teen suffered concussion, a skull fracture and a brain bleed and was flown to Wellington Hospital for specialist care.
He continues to suffer headaches, fatigue and lack of concentration as a result of the attack on April 5, 2021.
In court, a victim impact statement provided by the teen's father was read aloud.
"I'm so wild and angry at the harm you have caused my son. It was despicable, disgusting and deliberate," the man said.
"Picking on young teenagers is the lowest of low."
The man detailed how traumatic the attack was for his family, who were fearful the teen would die.
His son had a bright future but that was now hanging in the balance as he continued to suffer the effects of the incident.
"I don't think you actually realise the damage you have caused my family," the father said.
"I hope karma bites you hard."
Cornwall was appearing for sentence on six admitted charges, with the aggravated robbery being the most serious of the offending.
The other charges included assault on a person in a family relationship, assault on a police officer, escaping custody, intentional damage and breach of home detention.
Judge Hikaka said Cornwall, who has previous convictions for violence, showed a poor connection with family, the community and reality.
Cornwall was described as a pathological liar by his family, who also detailed troubling and violent behaviour displayed by him from a very young age.
A psychiatric report assessed him as having low cognitive functioning and a drug and alcohol report showed he had issues with drugs, including methamphetamine.
Judge Hikaka took a start point of five years' imprisonment before making allowances for guilty pleas and personal circumstances.
In the resulting sentence, Cornwall was jailed for three years and six months.