Sensex sees sharpest late-session fall since closing auction rollout

Sensex's indicative price fell more than 2,000 points during the Closing Auction Session before recovering; traders blamed CAS, but Sebi ruled out changes

The BSE Sensex on Thursday experienced the sharpest late-session volatility after the closing auction session (CAS) was implemented. Driven by sudden swings, the index experienced a change of -249 points between 3.15 pm and 3.35 pm, the highest since CAS was implemented on August 3, 2026. 

On the day of the first monthly expiry for the derivatives market since the exchange implemented CAS, Sensex closed 539 points lower at 76,933.6, down 0.70 per cent from its previous close. Much of the volatility occurred between 3.15 pm and 3.35 pm. 

Traders blamed CAS for the sharp swings, but the regulator remains firm on the new mechanism. Sebi Chairman Tuhin Kanta Pandey, speaking at a conference on Thursday, said there would be no changes to CAS. 

 

On the day of the weekly futures and options expiry on the BSE, the Sensex had traded above 77,100 throughout the day until 3.15 pm. During the CAS, however, the indicative price fell to as low as 74,988, a drop of around 2,000 points, before recovering some of the losses to close at 76,933. 

Traders said the index had not witnessed such volatility before and attributed the sharp swings to CAS. 

The 76,900 Sensex put option was trading at ₹4.70 at 3.15 pm. It then rose to ₹200 before closing at zero. Similarly, the 77,000 Sensex call option was trading at 327 before becoming zero instantly after the CAS session. 

“The primary function of the capital market is price discovery. Due to CAS the same had been taken away and the market has been turned into a casino. Randomness has taken over where actual trading during the market hours doesn’t matter at all and the last 10 mins define whether a trader will be actually in profit or not, especially option traders”, said a trader who works with a major broking firm. 

While the BSE Sensex remained volatile, the Nifty 50 closed 0.48 per cent lower at 24,090.85. HDFC Bank fell 

2.3 per cent, while Hindalco declined 2.75 per cent. 

Speaking at the sidelines of an event celebrating 30 years of NSE Clearing, the Sebi chief said: “We are not looking at any changes right now. The system is running as it is. Participation will increase as the brokers enable it in their apps. People will and will come to this market.”