Mistylea Erickson, who was planning on starting a new life with Mr Purdon in Western Australia before he died, said the offender deserved a harsher sentence.

"I knew he [the offender] wouldn't get much, but I thought he was going to get some time in jail," Ms Erickson said.

When asked if she would ever forgive the offender, who apologised on Monday, Ms Erickson said: "I can't say yes at the moment because I don't know if I can. Maybe five years down the track I can, but I don't know."

Mr Purdon's mother and stepfather, Cheryl and Paul Allen, said they were disappointed and concerned about what message the court sent to the community by not sentencing the offender to full-time jail.

"I think full-time detention would have been the better option," Mr Allen said.

"It's got to be a deterrent for others. [People] have got to realise that there are consequences for their actions."

"It just sends a [message] out there that people can just do what they want," Mrs Allen said.

Judge John Nield said the offender and another juvenile, neither of whom can be identified, chased Mr Purdon, of Raymond Terrace, and his two friends after 10pm at the Maitland Show on February 20 last year.

The offender punched Mr Purdon in the face causing him to fall and hit his head on the ground.

He died from head injuries.

The offender went home and told his family what happened and they telephoned police.

The offender pleaded guilty to manslaughter last April.

Judge Nield said a five-year prison sentence would have been appropriate, but he halved that because the offender pleaded guilty and had agreed to give evidence against the other juvenile.

The other juvenile, who was 15 at the time of the attack, will appear in Toronto Children's Court next month.

The offender will serve 18 months in periodic detention plus another year on parole.

Judge Nield said the offender was entitled to further leniency because he was publicly shamed when the Maitland Mercury named him in February.

Mr Allen said he approached the offender's father and neither he nor Mrs Allen held any ill-feelings towards the offender's family.

Mr and Mrs Allen spoke to the offender's parents after the sentencing and exchanged hugs before leaving the courthouse.

"They're good people," Mr Allen said.

"They were devastated when all this happened."

When asked if they could forgive the offender, Mr Allen said: "Oh, that's a big call, a big call."

The offender apologised to Mr Purdon's family on Monday.

There were a number of clashes, both physical and verbal, between various groups at the show on February 20, but Mr Purdon was not involved in any of them and was "an innocent victim", Judge Nield said.

"[Mr Purdon] did not provoke the offender," Judge Nield said.

"He did not have any time to defend himself against the offender's attack on him."