Cameron Smith's allergy to his community detention anklet has allowed him to be excused from completing his sentence.
A Corrections Department spokesman said it was believed to be the first time an electronically monitored sentence had been cancelled due to such an allergy.
There had been one other similar instance, but on that occasion the situation was alleviated by the offender wearing a sock.
"On this occasion, however, we tried that and the allergy persisted," the spokesman said.
Smith will do community work instead.
Confronted by the unusual situation in Napier District Court yesterday, Judge Geoff Rea told Smith: "One thing about this job, Mr Smith, is that something different happens every day. Someone who's allergic to the bracelets is a first."
Judge Rea said a medical certificate had confirmed Smith's allergy to the plastic anklet, and that Corrections consented to altering his sentence to one of community work.
He sentenced Smith, 43, to 150 hours' community work, and also fined him $2500.
"The downside to you, I suppose, is that if you get yourself into any more trouble you've ruled out any electronic monitoring," the judge told Smith.
Smith's lawyer, Derek Quilliam, told The Dominion Post that he had seen the injuries, which were now healing, "and they were pretty severe".
"He had bad scarring on both ankles because after the first one reacted they tried it on the other. It looked very painful," Mr Quilliam said.
Smith had been serving a sentence of six months community detention, imposed in Wellington District Court in September.
He had admitted 12 charges of assault on children and ill treatment of children over the previous year.
A police summary said Smith was very controlling and would belittle the boys, aged 13 and 11.
He was in a relationship with their mother but was not their biological father. He had the boys get up at 5.45am to do chores and would get angry if they were not done properly.
Smith kicked one boy in the hip and then slapped him several times on the head over chores he thought were not done properly.
The boys both sustained injuries, including swollen eyes and bruising. Last August, they called their grandmother from a friend's home, and she called police.
- The Dominion Post
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