The campaign manager for Republican presidential candidate Donald Trump will not be prosecuted in the US state of Florida on a misdemeanor battery charge for grabbing a reporter, the State Attorney's office in Palm Beach County said Thursday.

Corey Lewandowski was charged last month for grabbing a female reporter by the arm at a campaign event on March 8 in Jupiter, Florida.

At the time, Michelle Fields was a reporter for the conservative Breitbart News website and was trying to ask Trump a question after the event.

She later tweeted a picture of a bruise on her arm and claimed to have been yanked backward.

Trump has repeatedly come under fire for comments about women and the media, as well as violence, at his campaign events.

The Republican front-runner later questioned Field's account, standing by Lewandowski amid calls to sack him over the incident. At times, Trump mocked the reporter and accused her of exaggerating.

Police later released a video of the incident which appears to show Lewandowski pulling Fields back from Trump.

"Although there was probable cause to make an arrest, the evidence cannot prove all legally required elements of the crime alleged and is insufficient to support a criminal prosecution," said court documents filed by State Attorney Dave Aronberg.

'Reasonable hypothesis of innocence'

According to another prosecutor, Chief Assistant State Attorney Adrienne Ellis, Lewandowski "pulled Ms. Fields back" while she was attempting to interview Trump.

In a memo, she said Lewandowski could have thought Fields was "making unwanted physical contact with Mr. Trump."

"Mr. Lewandowski may have had apparent authority to assist in the protection of the candidate, specifically to maintain the 'protective bubble' around the candidate," Ellis wrote. "While the facts support the allegation that Mr. Lewandowski did grab Ms. Fields' arm against her will, Mr. Lewandowski has a reasonable hypothesis of innocence."

Fields quit Breitbart News shortly after the incident, accusing the website of not supporting her in order to maintain favorable relations with Trump. Several other reporters also quit.

cw/cmk (AP, Reuters)