Floyd Mayweather might've been throwing jabs this weekend, but Joseline Hernandez was handing out haymakers backstage ... landing several on Big Lex.

The former "Love & Hip Hop" star -- dressed in light blue -- was on hand Sunday during FM's exhibition fight against John Gotti III in South Florida ... as were a ton of other Zeus Network-connected reality stars, like Big Lex for example.

Lex -- once featured on Joseline's own reality show, "Joseline's Cabaret" -- was on the receiving end of a brutal beatdown during the boxing match.

The video of her taking a whoopin' is going viral on social media right now ... and for good reason. You see Joseline holding Lex in a headlock while she wails on her -- which got so violent and tumultuous, it actually ended up leaving BL flailing and topless.

Clearly, Joseline got the better of Lex in the moment ... eventually, the women were separated. However, Joseline wasn't done using her fists -- she continued to throw punches at a bunch of different people in the vicinity (even men) ... and seemed to strike at random.

At one point, an unknown woman walking by all the commotion threw a drink in Joseline's direction ... and then got chased out of the building once JH realized where it came from.

It's unclear what precipitated the brawl -- but it obviously had Joseline in a wild state.

This wasn't the only chaos in the building that night ... another brouhaha broke out in the actual ring itself, not between the boxers -- but between their teams and management. Gotti was disqualified in the 6th for continuous holding ... and yet, he continued to battle.

Floyd's team jumped in to stop him themselves ... and that spurred an all-out rumble. Safe to say the antics made it one of the craziest sporting events anyone's seen in quite a while.