A teenager has been sentenced to more than eight years’ detention after his previous court appearance was interrupted by being allegedly assaulted by someone related to his victim.

The teen stabbed Ahmed Iyow repeatedly with a large hunting knife by the side of the road in the southern Brisbane suburb of Acacia Ridge at 2.30pm on May 17 last year.

Ahmed Iyow died in hospital the next month due to infection and organ failure.

Justice Rebecca Treston said the teen had stabbed his friend in “virtually unprovoked circumstances” after an altercation in which Ahmed Iyow broke his phone.

“It could hardly be considered to have provoked your response. [The victim] was on the ground when you repeatedly stabbed him,” she said.

“You inflicted violence when the victim did not fight back.”

The teen had complained that he would lose his drug dealing contacts as a result of damage to his phone.

Justice Treston told the teen he had taken the life of a joyful young man and left his family with a devastating loss.

She said she took the alleged events of Monday last week into account, where the teen was allegedly assaulted in court.

The teen was due to face sentencing that day when a 22-year-old man allegedly stabbed him with a pen in the back before being restrained by court security.

The teen also pleaded guilty to possession of a knife in a public place and threatening violence.

The teen threatened a nearby resident who tried to break up the fight with Ahmed Iyow.

Justice Treston said the teen had been diagnosed with severe conduct disorder and anti-social traits.

He had arrived in Australia as a seven-year-old after his family fled war-torn Somalia.

He started using drugs and alcohol from grade 7 at school and was soon began selling drugs and became immersed in gang culture.

The teen was isolated and not attending school or employment at the time of the murder.

Justice Treston said the teen later told a psychiatrist he “found stabbing people enjoyable”.

“The protection of the community is a matter of great significance in a case like this,” Justice Treston said.

She said she had no option but to regard the teen’s offending as particularly heinous, with a sentence of up to 14 years.

“Context of gang violence and prevalence of knife offences leading to needless deaths calls for significant punishment,” she said.

The teen will be required to serve 70 per cent of his 12 years in detention.

The 22-year-old man accused of assaulting the teen in court is due to face Brisbane Magistrates Court on April 10.