TMZ Sports has obtained video of Conor McGregor and his entourage going BERSERK at the Barclays Center ... attacking a bus leaving the arena with several UFC fighters, including members of Khabib Nurmagomedov's team.
An object was thrown through one of the bus windows -- and we're told the damage left one fighter, UFC lightweight contender Michael Chiesa, cut up and bloodied.
Fighters were at the arena doing media ahead of UFC 223 ... and McGregor was videotaped by several witnesses cruising around the arena before the incident.