Solkan Donaczy threw just one punch during an argument outside a Port Kembla hotel, but it was enough to cause another man's death and leave his own life in ruins.

His cowardly king-hit from behind on Scott Mahoney and the victim's collapse to the concrete pavement were captured on security video.

In Wollongong Local Court yesterday, 28-year-old Donaczy, of Bland St, Port Kembla, pleaded guilty to Mr Mahoney's manslaughter outside Port Kembla Hotel in the early hours of March 17, 2007.

The court heard that on the previous evening, Donaczy had invited a group of friends to his house where they drank alcohol for about six hours.

At midnight the group decided to walk to the Commercial Hotel, where Donaczy began a conversation with the victim.

The two men exchanged words outside the hotel after it closed about 3am, then Mr Mahoney walked towards Port Kembla Hotel, a short distance away.

There was a confrontation outside the hotel and as Mr Mahoney began walking away he was punched in the left-hand side of the head and fell heavily.

Bystanders rendered first aid to Mr Mahoney until paramedics arrived, but he never regained consciousness and was pronounced dead at Wollongong Hospital about 90 minutes later.

Police arrested Donaczy at a Primbee house on March 19.

Magistrate Paul Johnson committed Donaczy to Wollongong District Court for sentence on August 29.