A former elite soldier called as a witness by Ben Roberts-Smith in his defamation case has rejected allegations the war veteran kicked an unarmed Afghan man over a cliff during a mission the two completed in 2012.

Mr Roberts-Smith claims he was defamed by false allegations of bullying, domestic violence and unlawful killings published in three newspapers in 2018.

One of the most prominent allegations, in the reports by The Sydney Morning Herald, The Age and The Canberra Times, involved a September 2012 mission in the village of Darwan.

The Victoria Cross recipient denies accusations he kicked a farmer named Ali Jan over a cliff following an interrogation before the unarmed and cuffed man was executed in a dry creek bed.

An ex-SAS soldier, who was in Mr Roberts-Smith's patrol during that mission, on Tuesday told the Federal Court of clearing compounds.

The witness, codenamed Person 11, said as they waited for a helicopter extraction, he moved into an agricultural area at a creek bed to clear it because it was near the helicopter landing site.

"Shortly after coming out of the dry creek bed, I identified an individual in amongst the corn and rest of the fields," Person 11 said.

"This individual was moving, [in] my assessment … in a very suspicious manner."

Person 11 told the court he saw the man carrying a radio, leading him to believe he was a Taliban "spotter" attempting to report on the Australian soldiers' movements.

"The individual appeared to be trying to remain concealed, noting our helicopters were on approach, and I assessed this person posed a direct threat to our extraction, so I engaged."

Person 11 said he heard gunfire behind him which he later learned was from Mr Roberts-Smith.

Person 11 said the man was about 15 metres away, estimating he shot "three to five rounds".

He said a "hasty" SSE (sensitive site exploitation), or search, was conducted on the body and the ICOM radio was recovered.

Person 11 was shown a photograph of the body and said he did not know the cause of blood on the person's face.

Mr Roberts-Smith's barrister, Arthur Moses SC, put it to him that the newspapers allege the man suffered injuries as his head hit a rock on the way down the cliff, after being kicked.

"I reject that allegation," he replied.

Person 11's evidence contradicts the account of a previous soldier witness for publisher Nine Entertainment, codenamed Person 4.

Person 4 told the court he saw a handcuffed man being held by Person 11 with his back towards a slope before he was kicked and "catapulted" backwards by Mr Roberts-Smith.

Person 4 recalled seeing the man's face strike a large rock and claimed that Mr Roberts-Smith directed him and Person 11 to drag the injured man towards a large tree, before Mr Roberts-Smith and Person 11 had a "quick conversation".

He said three shots rang out and when he turned around he saw Person 11 in a "position to shoot".

Person 4 claimed when the man's body was photographed, there was an ICOM radio with him, which was not on him while he was being questioned.

Last year, Mr Roberts-Smith told the court he climbed an embankment when Person 11 engaged the suspected Taliban spotter.

He said he heard shots and reacted to support his colleague.

Mr Roberts-Smith said the man's body was in a cornfield and while it was searched, an ICOM radio was found.

The trial, before Justice Anthony Besanko, continues.