According to the lawsuit, the R&B megastar spearheaded a beatdown of 4 men backstage following his Fort Worth, TX tour stop on July 20, as well as a security guard who claims he suffered injuries attempting to break up the ruckus.

Brown's attorney, Levi McCathern, tells TMZ Hip Hop ... he's suspicious about how fast the 50-page lawsuit was drummed up after the alleged brawl and claims the men who say they were beaten up were well enough to leave the venue without medical aid.

McCathern also says he believes there's a video of the incident and says he isn't afraid for it to surface ... telling us he thinks it'll be a key part of Breezy's defense. Whether a video actually exists though ... well, it's unclear.

He's playing coy for sure -- but the implication is ... yes, some sort of video does exist that might be able to help Chris' case.