Bondi Junction one-punch attacker claims he was defending friend, despite timeline gap

An Argentinian man accused of a one-punch attack on a Sydney street that left an Irishman in an induced coma for nine days is arguing that he acted in self-defence and was stepping in to defend a friend.

Adrian Martinez, 30, is currently facing trial at Sydney's Downing Centre Local Court, charged with recklessly causing grievous bodily harm over the punch which left Jason Cierans, 29, suffering from a subdural haemorrhage after his head hit the pavement.

Mr Cierans was transported to St Vincent's Hospital, where he was subsequently placed in an induced coma and had part of his skull removed.

Despite recovering significantly from the injuries, Mr Cierans suffered brain swelling and has experienced some negative health effects as a result of the attack.

Mr Martinez was walking along Bronte Road with a group of friends when Mr Cierans approached them and assaulted one of Mr Martinez's entourage, the court heard.

The fight followed an altercation at a 7-11 store just moments earlier, in which one of Mr Cieran's friends assaulted one of Mr Martinez's friends.

Mr Cierans friend, Ian O'Leary, was charged over that incident.

Mr Martinez does not deny that he punched Mr Cierans, but he denies being the aggressor, according to the Sydney Morning Herald.

"The defence says that Jason Cierans punched Mr Martinez's friend, Conrad, making him fall into a number of bins and then he turned and shaped up to two more of Mr Martinez's friends - Juan and Giorgio," Scott Corrish, Mr Martinez's barrister, said.

However, the prosecution claim that an eight to 10 second gap between the punch thrown by Mr Cierans and the one Mr Martinez delivered show that the punch was not an act of self-defence.