A man who fatally dropped a six-month-old baby on its head could have been an NRL star before he started taking the drug ice, his stepfather has told a NSW court.
George Cox says his stepson Jie Smith had been a quiet, promising young footballer in Gunnedah before moving to Newcastle to try out for the Knights.
"I thought he was going to be the next Greg Inglis," Mr Cox told Justice Helen Smith on Thursday during a sentence hearing for Smith in the Newcastle Supreme Court.
He was found not guilty by a jury of murdering the baby but pleaded guilty to the lesser charge of manslaughter.
Mr Cox said Smith's love of football began to fall away after being given the drug ice by his aunt in Newcastle.
"He just lost interest in his football and for most of his life that had been his life.
"I knew he smoked a bit of weed (cannabis) but didn't know about the harder stuff until later on."
Police had claimed Smith, 31, had been alone with the baby at New Lambton when the child was seriously injured, including suffering a fractured skull.
But Smith told the jury during a two-week trial in July that the boy's mother had repeatedly punched and shaken the crying baby about 2am on February 9, 2019, before leaving him with Smith after she had been given her share of the drug ice he had bought earlier.
Smith claimed he was holding the distressed boy when he likely suffered a seizure from the earlier attack and the boy slipped from his arms, causing him to hit his head on the ground.
He pleaded guilty to manslaughter after accepting he should have sought medical help for the child earlier and this had been gross negligence on his part.
The mother denied assaulting her son and claimed he was unharmed when she left.
Smith told the court on Thursday he was "embarrassed and ashamed".
"I wish I could have done more to stop this from happening," Smith said.
"There's not a day goes by that I don't think of that little boy. I also do have nightmares. It's something that's going to stick with me for the rest of my life."
The mother, who has four other children, told Justice Smith on Thursday she continued to struggle with the loss of her baby son.
"I feel destroyed, shattered and heartbroken," she said.
"I miss him more than anything.
"I know I wasn't the best mum, but I know I was a good mum. I would never hurt my baby or children."
During the trial, Smith told the jury he initially lied to police about what happened to protect the mother despite the fact they were only in a casual relationship based on drugs and sex.
He told police he had accidentally dropped the child and did not mention what the mother had done until four months later.
Specialist forensic pathologist Johan Duflou, called by the defence, said it was "entirely possible" Smith's version of events fitted in with the seriously injured child's condition when taken to hospital.
Professor Duflou said an earlier shaking and punching incident could have led to a deterioration in brain functioning and to seizures which could be a reason why the baby fell out of Smith's arms.
Justice Smith, who will sentence Smith on December 7, said there were two conflicting versions of what had happened and she might not be able to make any findings as to how the child's injuries were inflicted.