Nifty swings 2.2% on F&O expiry as SEBI weighs auction rule changes

India's Nifty index experienced a sharp 2.2% intraday slump during the monthly derivatives expiry on September 29, briefly falling to 22,267 before recovering, while Bank Nifty also declined during the closing auction session. The volatility stems from the Closing Auction System (CAS) introduced in August, which has caused price swings on expiry days. SEBI has proposed reverting to a volume-weighted average price for settlement and tightening auction rules, with brokerages supporting the changes to reduce distortions. The Nifty 50 closed down 0.28% at 22,716.2, and analysts identified 22,600 as a crucial support level. India's market underperformance is partly attributed to rising US Treasury yields and higher oil import costs, with the index down 5.7% in September.