The Sydney teenager who pierced the skull of Liam Knight with a metal pole has been sentenced to at least eight years.

Liam was one of about 70 guests celebrating the 18th birthday of his friend Harry Staples in Forestville in Sydney’s north in January last year when things went horribly wrong.

The then 16-year-old DS gatecrashed the party and scaled a high fence at the home and climbed onto the roof of a shed.

Angry and intoxicated, he began throwing building materials at partygoers.

One of four steel three-metre rebars that he threw into the crowd pierced Liam’s skull and lodged in his head.

In sentencing DS to a maximum of 12 years and six months over the attack on Friday, Acting Judge Ronald Solomon told Sydney’s District Court that the consequences for Liam were “catastrophic”.

“The degree of violence perpetrated by the offender was high and the degree of harm extreme.”

The court has previously heard Liam, 18, underwent five hours of life-saving surgery – leaving his “life in tatters”.

“DS has changed my whole life for the simple fact that he couldn’t get into a party,” Liam told the court during DS’s sentence hearing in June.