BENJAMIN Batterham had a legal right to chase and restrain the man who he found inside his Hamilton home in the early hours of Easter Saturday in 2016.
But when he tackled intruder Richard Slater, 34, outside a home in Cleary Street, held him down in a "choke-hold", repeatedly punched him in the head and ignored the pleas of Mr Slater, other neighbours and an off-duty police officer to let him up, Mr Batterham was "exacting some form of revenge" on Mr Slater, who had minutes earlier stolen a bag from his young daughter's bedroom, a jury has heard.
Mr Slater died the next day in hospital and his cause of death will be the crucial issue at Mr Batterham's murder trial, which began in Newcastle Supreme Court on Monday.
Mr Slater was a regular user of ice, had a "potentially lethal" level of the drug in his system at the time of his death, had a pre-existing heart condition and was obese.
Much of the trial will focus on the evidence of medical experts - including cardiologists, forensic pathologists and clinical toxicologists - who are divided over the role that the assault, the drug use and the pre-existing conditions played in causing Mr Slater's death.
"The ultimate question will be, given those conditions and given the nature of the assault, was the act of [Mr Batterham] a significant or substantial cause of the death of [Mr Slater]" Crown prosecutor Wayne Creasey, SC, said.
The other issue for the jury to decide is whether Mr Batterham had an intention to kill or seriously injure Mr Slater during his efforts to restrain him.
Defence barrister, Winston Terracini, SC, said the evidence was insufficient to convict Mr Batterham, now 36, of murder because there was never an intention to kill or seriously injure Mr Slater.
And in relation to manslaughter, he said, given the circumstances, Mr Batterham's conduct was neither "unlawful nor dangerous".
Mr Batterham was drinking and celebrating his birthday at home in Cleary Street about 3.20am on March 26, 2016, when he saw Mr Slater inside his house.
Mr Slater had stolen a bag from Mr Batterham's daughter's bedroom, but both Mr Batterham's daughter and his wife were not at home at the time of the break-in.
Mr Batterham chased Mr Slater about 330 metres around Hamilton, losing sight of him, calling the police, spotting him again, chasing him and then eventually tackling him to the ground, where the two men struggled.
During his opening address, Mr Creasey told the jury a number of neighbours in Cleary Street will give evidence that they saw Mr Batterham on top of Mr Slater holding him down, punching him in the head and abusing him.
"You mother-f---er, piece of shit, how dare you break into my daughter's room, she is only seven months old," Mr Batterham said, according to witnesses.
Another woman said she heard a man yell: "I'm going to crack your head like an Easter egg".
Mr Creasey said a number of those neighbours told Mr Batterham to let Mr Slater up, including an off-duty police officer who told Mr Batterham "let him go or he will die".
Mr Batterham was beginning to loosen his grip on Mr Slater when Mr Slater bit him on the webbing of his hand, enraging Mr Batterham who pinned Mr Slater again and punched him.
Mr Slater died the next day in John Hunter Hospital and Mr Batterham was charged with his murder.
"You may think that the accused intended to catch this man and he had a legal right to do that," Mr Creasey told the jury.
"He had a legal right to pursue and a legal right to restrain him. "But that doesn't give him the right to assault him and it doesn't give him the right to exact some form of revenge on the deceased and that is the case here."
Mr Creasey said if the jury were not satisfied Mr Batterham had the requisite intention to convict him of murder, then they could find him guilty of manslaughter on the basis that he committed a dangerous or unlawful act.
Mr Terracini said at no point did Mr Batterham have an intention to kill or inflict serious injury to Mr Slater.
"Just because you say you're going to belt someone or even in some instances say you're going to kill someone it's not literally what you're going to do," Mr Terracini said. "[Mr Batterham] is entitled to be very annoyed. "He is entitled to give chase in the circumstances on the night and hold him until the police arrive and you will hear that when the uniform police arrive he got off the deceased man almost immediately."
The trial, before Justice Desmond Fagan, is expected to run for about four weeks.