The jiu jitsu specialist and soon-to-be cage fighter was asleep in his Maitland home when the harrowing noises emanated from a neighbouring carpark early on Tuesday morning.

“I haven’t really heard screams like that before; they were pretty awful,’’ he said.

He jumped out of bed, still in his skins from training the previous night, and ran outside in time to be threatened by two men before they legged it.

And Mr Grayson gave chase, thinking they had broken into his car and stolen his work laptop.

In fact, the 27-year-old had helped foil what police allege was a vicious armed robbery of a woman who was punched in the face at least six times and threatened with a weapon.

Mr Grayson chased them down the street, got his hands on one of the suspects, put him in a martial arts hold, and waited for the constabulary.

“If he had not have turned up, who knows what could have happened,’’ Detective Inspector Mitch Dubovski said.

The woman, 40, had parked in the Moore Street carpark about 5.30am on her way to gym class, saw two men and waited a short time for them to leave before opening her door.

Police will allege it was then that she was set upon by one of the men, who threatened to stab her and punched her repeatedly in the face before stealing a bag she had with her.

She attempted to kick back and screamed – the same screams Mr Grayson heard.

The martial arts expert quickly appeared and chased the men towards Elgin Street, with the help of a council worker who had also come across the alleged robbery.

The suspects ran into a one-way street, and although Mr Grayson had struggled to keep up during the chase, he liked his chances once they had to run past him.

He tackled one suspect to the ground and grabbed at the second, taking a handful of his pants as they ripped and allowed him to escape.

“I am just a bit filthy that I didn't get the second one; I should have got him,’’ Mr Grayson said.

CCTV shows the men getting off an XPT service at Maitland train station about 4am. A Casino man, 24, has been charged with aggravated robbery. A second suspect, wearing dark clothing in the railway station footage, is still on the run.