The ugly scenes broke out at Bugmans Bar in Warhammer World, Nottingham just hours after the first day of tournament gaming.
Concerned staff dialed for help as violence flared, resulting in the arrival of a squad of Grey Knights and Inquisitor Coteaz who temporarily closed the bar.
Interrogations are now under way to discover what caused the tensions to boil over. Coteaz believes many of those responsible fled the scene prior to his arrival and has urged them to come forward for "light" questioning.
The bar manager who has refused to be named told Talk Wargaming "the minute they came in from the Hall and started chanting Blood for the Blood God! it all went off. Loyalist Marine players from the toilet end of the bar launched themselves into the fray and they began tearing chunks out of each other. Shields and weapons were stripped from the walls and one spectacled nerd was swinging on the chandelier slashing at will with his Necromunda range ruler. It was when I saw that 2nd edition metal dreadnought flying through the air I knew it had gone too far and someone was about to die. I called in the Inquisition."
He confirmed that no members of staff were injured and no damage was caused to the premises.
Coteaz said the bar was shut while body parts were carried out and the two possessed men were given Bolter treatment "out back".
A spokesman for the bar blamed rival army players for the violence that marred a successful tournament weekend and promised to install Gun Servitors to keep tensions under control in future.
Games Workshop took to Facebook to apologise to punters who were caught up in the row when it happened.
The message said: "We would like to apologise for the inconvenience caused last night but a big thank you to all those that returned to the establishment to help clean up the gore in time for Sundays session"