Caleb Plant Slaps Jermall Charlo In Face At Spence Vs. Crawford Weigh-Ins

Errol Spence and Terence Crawford ain't the only boxers fighting in Las Vegas ... Caleb Plant and Jermall Charlo got into it on Friday as well -- and the altercation between the two stars was wild.

You can see in video shot at T-Mobile Arena ... Plant and Charlo were backstage at the Crawford vs. Spence weigh-ins, when Plant charged at Charlo and slapped him right in the face.

Plant's hand connected so flush with Charlo's cheek, it actually made a loud sound that forced a gasp out of at least one bystander.

The two seemed to want to escalate things further ... but, thankfully, a security guard ushered Plant away from the scene -- which calmed everyone down.

It's unclear why Plant hit Charlo, but after the squabble was broken up, Caleb yelled, "Don’t you ever grab me by my motherf****in' face again like that, boy."

The two have had beef for a while ... with Plant calling out Charlo prior to his fight against David Benavidez in March.

At the time, he said he wanted Jermall if he couldn't see Canelo Alvarez next. Coincidentally, Canelo is next slated to fight Jermall's twin brother, Jermell, in September.