Buy a ticket and join the crowds at a game at Mohammedan Sporting Ground. If there's nothing scheduled while you're there, you might like to check if the stadium offers a tour of the facilities.
There's a charge to enter this sporting facility, which is situated in Kolkata. But there's loads more to explore around these parts than just Mohammedan Sporting Ground. Victoria Memorial, Eden Gardens and Salt Lake Stadium are also worth adding to your list.