Donald Trump Jr. went to U.C.L.A. on Sunday to talk about a central message of his new book: how liberals are trying to silence conservatives with claims of political correctness.
But it was a far-right group — unsatisfied with the conservative positions of the event’s organizers — that most conspicuously disrupted Mr. Trump’s talk.
The group that organized the event, Turning Point USA, had previously canceled the question-and-answer portion of the event because it suspected the far-right group might cause a disturbance.
On Sunday, in a raucous scene captured in widely viewed videos, some in the audience yelled and booed during the talk, interrupting Mr. Trump and demanding that he take questions.
At one point, when Mr. Trump contended that conservatives do not disrupt liberal speakers on college campuses, one person yelled out, “Q. and A.” Mr. Trump responded by saying that a Q. and A. portion sometimes gets hijacked by those looking for a “sound bite.”
“You have some people spreading nonsense, spreading hate to try to take over that room,” he said. “That’s the real issue.”
More yells followed. Kimberly Guilfoyle, a former Fox News personality who was also speaking at the event, responded, “You’re not making your parents proud by being rude and disruptive and discourteous.”
Ms. Guilfoyle, who is Mr. Trump’s girlfriend, then added, “I bet you engage and go on online dating because you’re impressing no one here to get a date in person.”
A spokesman for Mr. Trump declined to comment on Monday.
The exchange prompted some to suggest that the far-right group had forced the event, which ran for about 35 minutes, to be cut short. A listing for the event shows it was scheduled to last two hours. The remaining time was allocated for book signings, organizers said.
Turning Point USA, a nonprofit conservative youth organization, said in a statement Monday that “it was our organization’s call to cancel the Q. and A. portion days before the event, after we were made aware of a preplanned effort to disrupt the event.”
The conflict that unfolded Sunday appeared to stem from an ongoing campaign led by Nicholas J. Fuentes against Turning Point USA.
Mr. Fuentes hosts a show called “America First” broadcast on YouTube and other online platforms. He has argued for “Christian nationalism” and against immigration, and has criticized Charlie Kirk, the head of Turning Point USA, over Mr. Kirk’s views on immigration.
Mr. Fuentes, who attended the “Unite the Right” rally in Charlottesville, Va., in 2017 at which a man who had espoused white supremacist views fatally struck a woman with his car, has said that the First Amendment was not written for Muslims or immigrants, according to The Chicago Tribune, which interviewed Mr. Fuentes in 2017. He has also said that some members of the media should be hanged or sent out of the country for what he determined was intentional false reporting, The Tribune reported.
A message left with someone at a number listed for Mr. Fuentes was not immediately returned on Monday.
On his show Monday evening, Mr. Fuentes said his intention was not to disrupt the event at U.C.L.A. But he said the demonstration was successful.
On Sunday, he wrote on Twitter that the protest was not aimed at Mr. Trump, whom he called a “patriot.”
He said Monday on Twitter that the head of Turning Point USA “is a total failure that continues to be humiliated by real nationalist conservatives.”
“He’s lost control of his own events & he has lost the confidence of young Trump supporters,” Mr. Fuentes said. “It’s unfortunate Don got swept up in this but thank Kirk for that!”
Maggie Haberman contributed reporting. Sheelagh McNeill contributed research.