Mathew Neish has pleaded not guilty in the ACT Supreme Court to a charge of recklessly inflicting grievous bodily harm.

Neish, 26, is accused of attacking the man outside the Soul Bar in Woden in October 2010.

There is no dispute an incident occurred outside the venue, leaving the alleged victim with two black eyes and a fractured eye socket.

But in his opening statement, Neish's barrister, Jack Pappas, said his client had struck the complainant three times in self-defence.

The alleged victim told the jury he had been drinking with his girlfriend at the pub when he went to get cigarettes about 11pm.

On his return, he saw his girlfriend inside the bar arguing with another person.

The alleged victim said Neish then left the establishment and confronted him, shouting ''Go sort that bitch out.''

The man said he felt Neish's spit on his face and started moving backwards when he was punched in the head without warning.

The alleged victim told the court he covered his head with his arms and said, ''I don't want to fight you,'' but Neish continued to hit him another five times.

He said everything went black and he fell to the ground where he was struck a further four times before he lost consciousness.

The alleged victim's girlfriend entered the witness box on the second day of the jury trial.

The woman told the court she followed Neish, his girlfriend and a Soul Bar co-owner to a nearby car park after the incident.

She said Neish had come out of the shadows, grabbed her hair, pushed her to the ground and punched her in the side of the head about six times.

Under cross-examination from Mr Pappas, the woman denied she had followed the trio to the car park to confront them.

She also denied grabbing Neish's girlfriend by the jumper and punching her in the mouth.

The trial continues on Thursday.