The boy, who can't be named for legal reasons, broke free from corrective services officers and ran across the crowded court room before trying to attack his co-offender, Corey Loveridge.
"I'm going to kill you, you ****ing dog," the boy yelled as police officers and corrective service officers restrained him.
The boy was handcuffed to the jury dock ahead of the sentence hearing in the Supreme Court on Thursday.
The pair are facing a sentence hearing for the murder of a 17-year-old teenager who was stabbed multiple times in a brutal and unprovoked attack in December 2010.
Loveridge, 20, was found guilty of murder by a jury last April, while the teenager pleaded guilty at an earlier date.
Loveridge's trial heard the pair approached their victim, his brother and step-brother, as they walked to a service station, before attacking the youngest boy.
The victim, who also can't be named for legal reasons, screamed, "I haven't done anything to you", in his dying moments as his brothers desperately tried to get help.
He died from massive blood loss after he suffered 30 wounds - most of them stab wounds - all over his body including the chest, abdomen, heart, lungs, liver, neck and head.
Loveridge later told police, "I agree I did bash (him)," but he played down his role in the attack, blaming it on his co-accused.
Loveridge is a cousin of Kieran Loveridge, who killed teenager Thomas Kelly in an unprovoked attack at Kings Cross in July last year.
