Ratahi attacked Mr Scullin outside his home on November 30 last year after he came to the aid of another man involved in a confrontation with gang members.
When Mr Scullin got in between the men he was punched in the face by one of the group and Ratahi ripped off a piece of fence paling and hit him over the head.
Mr Scullin suffered a bloody nose and bruising and his body was found in the back yard of his home the next morning.
There was no evidence the assault contributed to his death
The driving offences were committed on December 14 and May 22 this year.
Speaking from Timaru yesterday, Mr Scullin's mother Moira Hazelwood said she was extremely disappointed about Ratahi's sentence.
" ... I feel 12 months' prison isn't sufficient."
She said her son's death had been a huge blow to his family and something she would never get over.
Mr Scullin had three young children aged 5 to 9, and a 19-year-old daughter from a previous marriage, who is due to have his grandchild on October 8.
Judge Phillip Cooper, who convicted and discharged Ratahi on the driving while forbidden charge, said a community-based sentence on the other charges would be inadequate deterrent response.
Particularly given Ratahi's prior convictions, including burglary and a breach of intensive supervision, he said.
Ratahi will be subject to six months release conditions requiring him to undergo counselling.
Another Tauranga, man Anthony Taikato, 32, accused of punching Mr Scullin in the head the night before his death had the charge withdrawn due to lack of evidence.
