A teenage father has been sentenced to a year's home detention for repeated assaults on his infant daughter that resulted in her legs being broken in five places.

The girl's mother told the court how her partner, James Hall, had always been willing to care for their daughter and she was shocked to find that he had been badly injuring her when alone with her.

Hall, now 20, was sentenced in the High Court at Napier yesterday after earlier pleading guilty to a charge of causing grievous bodily harm with intent to injure and a representative charge of causing grievous bodily harm with careless disregard.

The victim was his daughter, who was just four months old when admitted to hospital with injuries in March last year.

Staff found her left and right femurs were both broken, and there was an older break to her left tibia.

According to the police summary, Hall admitted that when alone with his daughter he "grabbed her left foot, pushed it back up so it was bending her whole left leg up behind the baby's back".

He said he knew what he was doing was wrong, but he just was not thinking. "He stated that once or twice he meant to hurt her by bending her leg back in blind anger - not realising what he was actually doing," the summary said.

He also said he squeezed her firmly against his chest three or four times.

The Crown sought a starting point of four years' jail. Hall's lawyer, Scott Jefferson, sought a starting point of 2 years.

Justice Mary Peters started at three years and three months. She reduced that for Hall's youth and his early acknowledgement of guilt, and arrived at 12 months' home detention. She also barred him from being with children under 10.

In imposing her sentence, Justice Peters said: "Home detention is not a soft option."

She did not impose community work on top of home detention as she felt it better that Hall complete his apprenticeship as a painter and decorator, so he could provide for his daughter financially.

The mother, whose name is suppressed, told the court she had known Hall since she was 15 and they were living as a couple.

Hall always offered to care for their baby if she was leaving the house "and never showed any signs of not being able to cope".

Their daughter was usually asleep when she left their home but was always awake on her return, even if she had gone for just five minutes,

The girl "would often cry when James held her. At the time I thought it was just because he was at work all day and they hadn't had the chance to form a strong bond yet. Now when I look back I realise it was because she was scared of him."

She had taken the girl to the doctor several times with injuries she was told might have been swelling from insect bites or bruising because her seatbelt was too tight.

"Now I know those bruises were from him squeezing her."