A former teenage speedway racing champion killed his sister's abusive boyfriend "out of panic and fear", a judge has been told.
After stabbing his victim Jesse Tattersall twice, Tyler King told his sister, "No one's going to f***n hit you again, no one's going to hurt you again" before stabbing Tattersall a third time.
Prosecutor Brendan Queenan told Newcastle Supreme Court on Friday that King was showing his sister Tenille how he intended to kill Tattersall because of what he had been doing to her.
But defence barrister Peter Krisenthal argued King would not have let Tattersall leave the duplex and try to get help from a neighbour after being stabbed if he had intended to kill him.
Mr Krisenthal said King, 27, of Budgewoi, who pleaded guilty to the manslaughter of Tattersall, 33, at Hamlyn Terrace on September 8, 2022, was remorseful and understood the impact his actions had had on his victim's family.
"The offence was reactionary, borne out of panic and fear," the defence barrister said.
"There was, on any objective analysis, hostility and volatility coming from the deceased and his behaviour was unpredictable and aggressive."
Mr Krisenthal said King had been a talented speedway racer who left school and travelled overseas to compete at the age of 15 on a one-year contract but didn't have the success he expected.
He said King returned to Australia and his life spiralled out of control when he became addicted to drugs.
Tattersall, a father of two, was killed when he arrived at Tenille's home just after 8.10pm after she had told him her brother was upset because she was choosing Tattersall over her family.
Tattersall kicked open the front door, grabbed Tenille by the back of the head and punched her in the face.
He started dragging Tenille through the living room when King pulled him off his sister.
Tattersall slammed King's head through a plasterboard wall and told him, "You should see what I do to her (Tenille) in the bedroom".
King grabbed a knife from the kitchen as the pair fought and stabbed Tattersall three times as Tenille tried to stop him.
Tattersall stumbled out of the house and collapsed at the front of a neighbour's house.
Paramedics could not revive him.
King and his then girlfriend, Maddison York, called an Uber after fleeing but were later found at Gorokan.
York has pleaded guilty to being an accessory after the fact to the killing.
Tattersall's mother Donna said in a victim impact statement King had no right to take her much-loved and incredibly precious son's life.
Mrs Tattersall said she arrived at the scene to see her first born son "lying on that cold concrete covered in blood with a number of paramedics attempting to save his life".
"These images haunt my thoughts as do images of my boy lying on a cold, steel autopsy table."
Justice Natalie Adams will sentence King and York on May 23 and ordered York be released on bail after she had already spent 19 months in prison following her arrest.
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