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Florida prosecutors said Thursday that they wouldn't charge Republican presidential candidate Donald Trump's campaign manager with battery in an incident involving a reporter.

Florida State Attorney Dave Aronberg said in a news conference that Corey Lewandowski wouldn't face charges for allegedly grabbing the arm of reporter Michelle Fields while she was trying to ask Mr. Trump a question at an event in Florida in March.

Mr. Aronberg made clear that he believed there was ample evidence that some physical contact between the two occurred, despite earlier denials from the Trump campaign. But the prosecution also said that in a situation involving a political candidate being protected by the U.S. Secret Service, close aides are often given some latitude to help keep people away from the candidate.

The evidence "is not strong enough to meet the legal burden of a reasonable likelihood of a conviction," Mr. Aronberg said.

Ms. Fields, who at the time was a reporter for the website Breitbart News, filed a complaint with the police that resulted in a misdemeanor charge of simple battery against Mr. Lewandowski in March. Mr. Trump has stood by Mr. Lewandowski, a 42-year-old political operative and former New Hampshire state police officer who has helped propel Mr. Trump to the top of the GOP presidential field.

The incident came amid mounting public concern over fights and assaults at packed Trump rallies, where protesters often face off with supporters. The Trump campaign has done little to stop violent encounters, according to critics. Mr. Trump has said he doesn't encourage violence.

In a statement Thursday, the Trump campaign said: "Corey Lewandowski is gratified by the decision to drop the misdemeanor charge and appreciates the thoughtful consideration and professionalism by the Palm Beach State Attorney and his staff who carefully reviewed this matter, as well as Mr. Trump's loyalty and the support of his colleagues and family during this time. The matter is now concluded."

Mr. Lewandowski has repeatedly denied that he touched Ms. Fields, though video of the incident appears to show him yanking her away from the candidate. The encounter between Ms. Fields and the Trump campaign manager was also witnessed by a Washington Post reporter who wrote a story describing the incident.

Shortly after the incident occurred, Mr. Lewandowski called Ms. Fields "delusional" in a tweet, saying: "I never touched you. As a matter of fact, I have never even met you." His attorney Brad Cohen backed away from that claim on Thursday, acknowledging that some physical contact seems to have occurred.

"Would he apologize for having any contact with her? Certainly, he could. I don't know what he's going to do," said Mr. Cohen in an interview with CNN on Thursday. He said Ms. Fields's statement to the Blaze website that she was planning to pursue a civil lawsuit could complicate any apology.

Mr. Cohen said that as part of his defense of Mr. Lewandowski he provided prosecutors evidence that the Secret Service had been attempting to move reporters away from Mr. Trump before the alleged encounter. Mr. Cohen also said he provided a sworn affidavit from a former FBI agent who said Mr. Lewandowski's behavior was justified.

Ms. Fields didn't respond to a request for comment, but she took to Twitter to express her disappointment in the Florida prosecutor's decision not to bring charges and anger that she hadn't been informed directly ahead of the announcement.

"For those asking, office of prosecutor asked 2 weeks ago if I'd be ok with an apology from Corey. I said ya but haven't heard back about it," she wrote.

Following the incident, Ms. Fields resigned her position with Breitbart after other employees at the website cast doubt on her account. Several other reporters also left the news outlet, expressing disappointment with the way the situation was handled.

Mr. Aronberg said that the evidence clearly pointed to the fact that Mr. Lewandowski was involved in a physical altercation.

"There is no reasonable doubt that Mr. Lewandowski pulled Ms. Fields back as she was attempting to interview Mr. Trump," said Mr. Aronberg.

Mr. Aronberg, a Democrat, said that Mr. Trump had been in contact with their office and "urged us to do the right thing"—alleging that Ms. Fields had touched him before the alleged contact between her and his campaign manager. He added that Mr. Trump's involvement had no bearing on the office's decision not to bring charges.

Corrections & Amplifications: Corey Lewandowski is 42 years old. An earlier version of this article incorrectly stated he was 41. (April 14)

Write to Byron Tau at byron.tau@wsj.com

(END) Dow Jones Newswires

April 14, 2016 22:25 ET (02:25 GMT)

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