'Below Deck' Star C.J. Lebeau -- Smile, You've Just Been Arrested for Assault

11:25 AM PT -- Law enforcement sources tell TMZ ... Lebeau allegedly got into a physical altercation with his fiancee and "took her to the ground."

We're told the woman told police Lebeau choked her ... but admits she struck him as well. Sources tell us Lebeau had a scratch on his face.

As for the defacing property charge -- we're told Lebeau is accused of breaking the woman's cell phone during the incident.

Lebeau is still in custody.

Bravo reality star C.J. Lebeau was arrested for assault in Arizona yesterday, TMZ has learned -- but you could barely tell from the way he was grinning in his mug shot.

FYI -- Lebeau is a marine engineer on the new reality show "Below Deck" ... which follows a bunch of good looking people who work on a fancy yacht.

The details surrounding Lebeau's arrest are sketchy at best -- but we know he was popped around 1AM Monday morning in Phoenix and charged with intentional assault and defacing property (less than $250 worth).

We also know Lebeau is described on Bravo's website as a marine engineer with a "rebellious side." Think Jacques Cousteau meets James Dean meets Camille Grammer.

Not So Fun Fact: It's not C.J.'s first run-in with the law, he has an open case in Arizona stemming from a marijuana-related arrest in May ... he's a rebel after all.

Bravo had no comment.