Hayden Panettiere's BF Brian Hickerson Allegedly Heckled Over Her Death, Watch Video

Brian Hickerson and his brother Zach may have been getting heckled about Hayden Panettiere before their wild bar brawl erupted ... and video obtained by TMZ shows just how chaotic things got.

An eyewitness tells TMZ ... Brian and Zach were drinking and hanging out in the back of the Greenville, South Carolina restaurant Saturday night when another table recognized Brian and allegedly started bad-mouthing the brothers over Hayden's death.

We're told the table had about five middle-aged people ... and a couple women from the group repeatedly walked over to Brian and Zach's table.

The witness says they couldn't hear what was being said ... and weren't sure if the women were asking questions about Hayden or trying to calm things down after the men at their table started mouthing off.

Either way, we're told things eventually boiled over when Zach approached one of the men and got in his face.

The eyewitness says Zach and the man started grabbing each other and moved toward the bar ... where other people quickly jumped in.

That's when things got chaotic ... people were yelling and holding each other back, glasses were thrown or knocked to the floor, a table got pushed over ... and the witness says Brian threw a chair during the melee.

We're told Brian also ended up with a cut on his face.

As we reported ... police later responded to the restaurant, where Brian and Zach were both detained.

Brian was ultimately released without being arrested ... while Zach was busted for disorderly conduct after police said he was highly intoxicated and yelling profanities -- he remains at Greenville County Detention Center and is being held without bail.