Down 0-1, Mohun Bagan midfielder Syed Rahim Nabi had to be hospitalised in the half time after being hit on the face by a missile, forcing the team management to come off the field in the second half.
It all started after East Bengal drew the first blood through Harmanjot Khabra in the 43rd minute from a Mehtab Hossain freekick.
The highly charged-up game snowballed into madness soon after Mohun Bagan's star player Okolie Odafa was sent off by referee Vishnu Chauhan for showing dissent.
As soon as the Nigerian was sent off, Mohun Bagan fans started to hurl missiles, one of them hitting Nabi's face.
There was more drama in store when Mohun Bagan left the field, forcing the match to be called off.