One of New Zealand's most acclaimed sportsmen has been sentenced to three years in prison after a fraud in which he stole and gambled away $450,000.

Three-time softball world champion and former Black Sox star Dion Nukunuku embezzled the money from his employer, Tower Insurance, and then splurged it at the TAB.

"This is a world [class] athlete who had a lovely family and now he has lost everything," said his lawyer Richard Earwaker. "It has been a spectacular fall from grace. He is penniless and he is now in prison."

Using his own name and the names of genuine Tower customers, Nukunuku submitted false insurance claims and then used the company's computer systems to write out false cheques to himself. He sometimes used computers that other staff had been logged on to.

The offending came to light only after Nukunuku, who has two children, was made redundant from Tower.

Earwaker told the Auckland District Court this week that his client was ashamed of his actions.

"Dion is extremely sad and remorseful - he said if he could change it, he would," Earwaker told the Herald on Sunday.

Tower sought reparation, but Earwaker said all the money had been gambled away at the TAB.

The court was told that Nukunuku stole the money over two periods - $47,355 was taken between March 2002 and April 2004 when he was a claims manager; and $402,200 was taken between April 2007 and February of this year when he was technical claims manager.

In total, he filed 46 false claims, using the names of 16 genuine policy holders plus his own.

Earwaker said Nukunuku had "known about gambling all his life" but it became a problem for him seven years ago. "In his 30s, it became a real issue."

Nukunuku's wife Anthea Gabriel had left him about three years ago - before the second period of offending. "Things got worse for Dion after that [his wife's departure]. Things just spiralled out of control and instead of getting help, he withdrew and gambled even more. It is so self-destructive."

Earwaker said Anthea knew nothing about his offending.

"She had no idea and neither did anyone else. That's part of the problem with gambling. It is very insidious.

"It was like a self-destruct mode really and it shows that no matter how successful you are, if you are susceptible to gambling and it gets a hold over you, it is very hard to stop."

Tower has obtained a summary judgment against Nukunuku for the amount owed, but a new legal battle is looming between the company and Anthea and Nukunuku's former mother-in-law, both of whom apparently have interests in Nukunuku's former family home.

"Neither the mother-in-law nor his ex-wife knew anything about his [offending] - that's why it's being defended," said Earwaker.

"The facts I know are that none of the money was used to enrich anybody else ... the money that was stolen was gambled away."

Earwaker said Nukunuku had now sought help for his gambling addiction. He said he hoped to eventually help others who found themselves in similar situations. "He was a great coach, too, but he pulled away from that because of the personal shame.

"This whole thing has been a tragedy all round. It's a message in terms of how dangerous and powerful gambling can be."

* Dion Nukunuku

Age: 39

Made his Black Sox debut in 1990.

Softballer of the Year, 1993.

Three-time world champion - 1996, 2000, 2004.

Hit his first home run for the Black Sox during his last at-bat in the 2004 world championships - a famous photograph shows him rounding the bases and pointing to his children in the grandstand.

Softball personality of the year, 2007.