Ben Roberts-Smith allegedly threatened a fellow SAS soldier he would get a "bullet in the back of the head" if his performance didn't improve, he told the Federal Court.
Thereafter the sergeant codenamed Person One said of his 2006 first deployment in Afghanistan that not only was he concerned about the Taliban, but he was looking "over my back," worrying "about people in my squadron".
The decorated soldier told the fresh trooper during pre-deployment training together he didn't think he had the "required skills" for Afghanistan, he said on Thursday.
"He also said that he was going to do everything he could within his power to have me removed from the team and get one of his colleagues to replace me."
He said the verbal and physical bullying worsened after a mission in the Chora Valley in June 2006.
Person One said he viewed an unarmed Afghan below the rocky outpost where he was keeping watch, but did not "engage" and draw noise to their secret location.
Soon after he heard suppressed gunfire shots from Mr Roberts-Smith's and the late Sergeant Matt Locke's weapons.
Later that evening Person One opened fire on what he thought was a moving target, but was prevented several times due to "stoppages" from his weapon that had not been oiled.
Mr Roberts-Smith's barrister Bruce McClintock SC said this failure could have "led to the deaths of you and five other SAS soldiers".
"In extreme circumstances yes," Person One said.
Following the mission, a written log entry stated the slain Afghan was armed with an AK weapon, and "ready to fire," statements which Person One says he did not observe.
For two months the still serving special forces soldier received declining performance reviews he attributed to Mr Roberts-Smith's continual intimidation.
On the small base where they came into contact "relatively often" this included spitting "on the ground in front me," and slamming doors in his face, he said.
He recalled one meeting in a team room.
"(He said) words to the effect: 'If your performance doesn't improve in the next patrol you're going to get a bullet in the back of the head'," he said.
"It made me fearful for my own personal safety. It made me lose more confidence. It made my performance worse."
After he told SAS colleagues about the alleged threat, he said Mr Roberts-Smith "stood over me (and) looked down on me".
"He said 'if you're going to make accusations c*** you better have f***ing proof'."
The Victoria Cross recipient is suing The Age, The Sydney Morning Herald and The Canberra Times for defamation and denies their reports that he committed war crimes and murders in Afghanistan between 2006 and 2012.
The 43-year-old categorically denied the accusations of bullying while giving evidence last year.
He said Person One just wasn't a "very good soldier" who wanted to cover up his poor performance.
The newspapers' barrister Nicholas Owens SC read out a number of Person One's performance logs after he was moved on from Mr Roberts-Smith's troop, with vastly improved results.
Person One said he didn't understand why the bullying continued for years, citing another incident where he was pushed square in the chest-plate outside the "ready room".
"Get out of my way c*** or I'll kill you," he recalled him saying.
Years later he heard from other patrol commanders the former SAS corporal had been rubbishing his credibility, saying he was "an incompetent soldier, a coward, and ... didn't deserve to be in the regiment".
Mr McClintock said Person One was incompetent, and once "had to be asked three times" to drop his lunch of noodles, to escape the enemy.
"I don't recall it like that," he said.
The trial continues.
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