A Manhattan judge, Donald J. Trump on Wednesday briefly ordered the witness stand, accusing a law writer of violating a gag order containing critical comments that appeared to be aimed at him, and later fined him $10,000.

Mr. The judge presiding over Trump’s civil fraud trial, Arthur F. Mr. Engoron sought an order barring him from conferring with court staff. Mr. Trump’s comments were directed not at the writer he previously attacked, but at his former lawyer, Michael D. Cohen said he had mentioned a witness.

From the point of view of Mr. Trump, wearing a navy suit and holding back the length of his usual monologues, said when he wasn’t talking about author Alison Greenfield, he “can be unfair, and I think she’s very biased. Against me.”

Mr. Trump left the stand after about three minutes. Justice Ngoron said he found the former president not credible and imposed the fine.

The episode is remarkable and totally unexpected: Mr. Although Trump has engaged in his own defense outside the courtroom, he hasn’t testified in open court in more than a decade, and when he did, the judge found against him. For the former president, who is expected to testify later in a civil fraud trial and has been indicted four other times, it was a grim preview of what might await.

During a break in the case on Wednesday, Mr. Trump called Judge Engron a partisan — something that is allowed under the order. But he continued, “A very partisan person is sitting with him. Perhaps more discriminating than him.

After the break, the judge expressed concern that the overheated atmosphere in the courtroom could pose a real danger.

“I’m very protective of my staff,” Judge Engoron said, “I don’t want anyone to get killed.”

Mr. Trump’s lawyer, Christopher M. Mr. Kiss, the former president testifying for the second day. Mr. Immediately after Trump’s opening remarks, Mr. He clearly referred to Cohen as a “discredited witness.”

The judge replied that the target of the comments seemed clear to him and, after lunch, called the hearing.

Mr. Trump took the witness stand and faced the courtroom for a brief hearing from the judge. Judge Engoron asked if he had referred to Ms Greenfield as a “partisan” in the past and if he had always referred to Mr Cohen as “Michael Cohen”. His lawyers, from the defense table, said Mr. Mr. Trump They assured the judge that they had more derogatory ways to refer to Cohen.

After Judge Engoron imposed the fine, the trial resumed and Mr. Trump’s lawyers, Mr. Cohen was forced to admit that he had lied on previous occasions. Soon, Mr. Another lawyer for Trump, Clifford S. Robert, Mr. Given Cohen’s contradictions, he called for an immediate verdict. Judge Engoron denied the request, and Mr. Trump leaned back in his chair and left the courtroom.