Craig Johnson, 22, pleaded guilty in Wollongong Local Court last week to a charge of recklessly causing grievous bodily harm over the June 4 incident, which left the victim's jaw so displaced one row of his teeth ended up in the middle of his throat.

However, when interviewed by police, Johnson said he had no memory what he'd done, telling officers he was a diagnosed epileptic and suffered short term memory loss.

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A set of agreed police facts tendered to the court reveal a large group of people were gathered on Woonona Beach for a party when an argument broke out between Johnson and another person late in the night after one of the guests threw a beer bottle into the darkness, causing it to smash.

Partygoers soon splintered off into different groups, including the witness and one of his friends, who decided to walk back to their car with the intention of leaving the gathering.

The victim's friend told police they were almost at the car when Johnson approached them from behind and began yelling at them, saying "do youse (sic) have a problem?"

The friend said "no we don't, we're leaving".

The victim said nothing during the brief encounter, however the agreed facts said Johnson grabbed hold of him out of nowhere and punched him in the face.

The victim grabbed hold of his jaw in pain before he and his friend fled to the safety of their car.

By the time they got into the vehicle, the victim was bleeding from the right side of his cheek, was spitting out "large chunks of blood" and was dizzy and feeling sick.

"The victim knew something was wrong with his jaw because his left side teeth were now in the middle of his throat," the police facts said.

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The victim drove himself to Wollongong Hospital where it was discovered he had multiple jaw fractures. He underwent surgery to have plates fixed into his jaw.

The court heard he continues to experience numbness to the chin area from nerve damage and hearing loss in the right ear.

Police were scathing of Johnson's behaviour in the fact sheets.

"The assault on the victim was completely unprovoked and unexpected," they wrote.

"The victim was completely blindsided by [Johnson's] one punch attack on him."

The victim reported the incident to police a day later.

Johnson was arrested on June 16 and taken to Wollongong Police Station. During an interview he admitted being at the party but said he had no memory of assaulting anyone.

Johnson will be sentenced on November 10.

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