Cassius Turvey, a 15-year-old Noongar Yamatji boy, died in hospital 10 days after prosecutors say he was chased, knocked to the ground and "deliberately struck to the head" with a metal pole in Perth's eastern suburbs on October 13, 2022.
Aleesha Louise Gilmore, 23, her boyfriend Jack Steven James Brearley, 23, and his mates Brodie Lee Palmer, 29, and Mitchell Colin Forth, 26, are on trial, charged with murdering Cassius.
In an interview with police after his arrest before Cassius died, Brearley admitted stepping on and punching the teen but denied he struck him with a pole.
"I only punched him once or twice that was literally it," he told detectives in the video of the interview shown to the WA Supreme Court on Wednesday.
"He was crying ... He said sorry, sorry, sorry, please stop."
Brearley said he was "just trying to stick up for my family with my fists".
The court was also shown a video of Brearley's arrest, in which he told officers a group of young people with knives got off a bus and were headed to the home he shared with Gilmore and her family.
Arrested at that stage on suspicion of assault causing bodily harm and unlawfully wounding Cassius, he told police: "I was attacked first".
"He stabbed me first three times across my leg," he can be heard saying in the police body-worn camera footage played for the jury.
"I stepped on his head and no pole involved or nothing."
Brearley told the officers the teen "was on the ground and he was just slashing my legs".
"Yeah I lost the plot but he had a knife and was stabbing me."
In the later interview with detectives, Brearley also told detectives there were 20 armed "kids" mouthing off at him and he ran at them.
"One tripped over ... and his mate threw him the knife and he got the knife and my foot was like this on his head ... and I just punched like three times," he said as he repeated his version of events, which changed as the interview wore on.
"I pushed him and the knife was in the mud and I stamped on it and it was gone."
Brearley also said a group of people had threatened to "run through" his home, break his bones and "bash my missus".
"What am I supposed to do? ... He pulled a knife on me ... He stabbed me and that's his fault," he said.
"I will admit I did punch him, I punched him max twice while my foot was on him."
Brearley said he, Forth and another mate had been following the bus in his friend's "monster" Ford ute after being alerted to a group of people headed to his home.
Asked who the other friend was he said: "I'd rather not say. He's a scary person".
"They were just waving bats and poles saying 'come on, we're ready, we're ready and I was like Mitchell, you better help me if they come to my house," Brearley said of the group.
"All these kids start pulling out weapons and s*** and start running in the bush towards my house.
Brearley said he chased "pretty much the fat one and he just stopped ... I pushed him".
"His mate yells 'chuck me the knife' and his mate chucks him the knife and I said 'are you going to use it'?" he said.
"If someone is gonna mob my mates I'm gonna stand by my mates".
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