Two brothers have admitted involvement in a violent assault and kidnapping in the north-eastern suburbs of Adelaide on Christmas Day in 2007.

Their identities are suppressed because one was a youth at the time.

The District Court was told the brothers from Syria used phone messages to lure their victim and his friend to netball courts at Golden Grove early on Christmas morning.

With at least two others, they savagely beat both men, tied them up and put one in the boot of their car.

He was later dumped near Gumeracha in the Adelaide Hills.

A lawyer for the elder brother said the attack was in response to racial vilification, including having the words 'Allah is dead' sprayed on their car.

She said the accused feared for their family's safety because the victim allegedly stole one of their cars and had keys to their house and businesses.

The court was told a third party recorded the bashing because someone involved accidentally made a telephone call during the fight.

There will be more submissions on penalty next week.