LOUISVILLE: A federal judge has rejected Donald Trump's free speech defence against a lawsuit accusing him of inciting violence against protesters at a campaign rally.

The president's lawyers sought to dismiss the lawsuit by three protesters who say they were roughed up by his supporters at a March 2016 rally in Louisville.

Mr Trump's lawyers contend that when the candidate said "Get 'em out of here", he did not intend for his supporters to use force.

Two women and a man say they were shoved and punched by audience members as Mr Trump directed them from the podium.

Much of it was captured on video and widely broadcast during the campaign, showing the Republican pointing at the protesters and repeating "get them out".

Judge David J Hale, in Louisville, ruled that the suit against Mr Trump, his campaign and three of his supporters could proceed.

Judge Hale found ample facts supporting allegations that the protesters' injuries were a "direct and proximate result" of Mr Trump's actions.

"It is plausible that Trump's direction to 'get 'em out of here' advocated the use of force," Judge Hale wrote.

Kashiya Nwanguma, Molly Shah and Henry Brousseau allege that they were physically attacked by several members of the audience, including Matthew Heimbach, Alvin Bamberger and an unnamed defendant they have yet to identify.

Mr Bamberger later apologised to the Korean War Veterans Association, whose uniform he wore at the rally.

He wrote that he "physically pushed a young woman down the aisle toward the exit" after "Trump kept saying 'get them out, get them out", according to the lawsuit.

Mr Heimbach sought to dismiss the lawsuit's discussion of his association with a white nationalist group and of statements he made about how Mr Trump could advance the group's interests.

The judge declined, saying such information could be important context when determining punitive damages.

The judge also declined to remove allegations that Ms Nwanguma, an African-American, was the victim of racial, ethnic and sexist slurs from the crowd at the rally. This context may support the plaintiffs' claims of negligence and incitement by Mr Trump and his campaign, the judge said.

"While the words themselves are repulsive, they are relevant to show the atmosphere in which the alleged events occurred," he wrote.

Lawyers for Mr Trump and his campaign argued that they cannot be held liable because they had no duty to the plaintiffs, who assumed the risk of injury when they decided to protest at the rally.

The judge countered that under the law, every person has a duty to every other person to use care to prevent foreseeable injury.

"In sum, the court finds that plaintiffs have adequately alleged that their harm was foreseeable and that the Trump defendants had a duty to prevent it," the judge ruled, referring the case to a federal magistrate, Judge H Brent Brennenstuhl, to handle preliminary litigation, discovery and settlement efforts.