India's Sensex and Nifty dip as new NSE closing auction sparks volatility ahead of RBI policy

On August 4, 2026 the BSE Sensex fell 210.08 points (‑0.27%) to 78,428.95 and the NSE Nifty 50 slipped 159.40 points (‑0.64%) to 24,614.90, ending a four‑session rally. The decline was linked to the National Stock Exchange’s newly introduced Closing Auction Session (CAS) for futures‑and‑options‑eligible shares, which introduced extra price‑discovery volatility and widened the usual Nifty‑Sensex divergence.

The CAS turnover was dominated by the NSE, accounting for Rs 1,542.4 crore (99.4% of total), while the BSE contributed Rs 9.4 crore. Actively traded stocks in the auction included Infosys, ICICI Bank, Bharti Airtel, Reliance Industries, HDFC Bank, Bajaj Finance, TCS, Mahindra & Mahindra, SBI and Wipro. Analysts described the market reaction as “teething issues” as participants adjusted to the new mechanism.

Investor sentiment was also shaped by broader cues: falling Brent crude to around $78 per barrel, strong global equity gains and anticipation of the Reserve Bank of India’s monetary‑policy decision on August 5. The RBI was expected to keep interest rates unchanged, a view that helped sustain buying in realty, auto, energy and public‑sector banking stocks, while healthcare and pharma lagged.

Overall, the market’s cautious stance reflected the combined impact of the new closing‑price auction and the pending RBI policy outcome.