Raz B's brother Ricky Romance claims he was ambushed at a concert in Atlanta last night ... and Ricky says the man responsible for the attack is rapper Yung Joc.
Ricky tells us, Raz was scheduled to perform last night at the Salute the DJ's Award Show -- but he never made it to the stage.
According to Ricky, Joc's security team stopped Raz in his tracks and refused to let him perform -- all because Raz publicly dissed Yung Joc in a song a few months ago.
Ricky tells us he tried to help get his brother past the hired muscle ... but Joc's security wasn't having it -- and roughed him up pretty bad instead.
Ricky claims he suffered some nasty cuts to his head during the melee -- before he and Raz were both forcefully thrown out of the Atrium Event Center (see video).
No police report was filed. Yung Joc had no comment.
Thanks to Insaneradioatl.com for the clip.