Why did Sensex rebound by 800 points within an hour today?

Sensex on Tuesday rebounded from early losses, rising 800 points within an hour during afternoon trade. The surge, from 73,999.17 to 74,807, was driven by buying in heavyweight stocks and short covering, as traders rushed to close their positions ahead of Nifty 50 derivatives expiration. Short covering occurs when investors buy back shares to close out previously opened short positions.