The Securities and Exchange Board of India (SEBI) has barred two entities from accessing the securities market for alleged manipulative trades during the closing auction session (CAS).

These are Copthall Mauritius Investment and Mansi Share & Stock Broking in a matter related to such trades during CAS on Sensex expiry at BSE.

Further, SEBI has directed the impounding of wrongful gains of Rs 3.67 crore by these two entities.

Copthall Mauritius Investment at Rs 2.96 crore and Rs 71.64 lakh from Mansi Share & Stock Broking, and prohibited them from participating in the CAS in the equity segment, directly or indirectly, or from placing, modifying or cancelling orders during the CAS until further orders. For Mansi Share & Stock Broking, the ban applies only to its proprietary trading account.

SEBI Chairman, Tuhin Kanta Pandey, has earlier warned that SEBI would take swift and stringent action against anyone attempting to manipulate the stock market’s new Closing Auction Session (CAS).

The new mechanism gives the regulator stronger tools to identify potential manipulation than the earlier system based on volume-weighted average price (VWAP), he said.

“If people do manipulation in CAS, then we will take strict action and do it immediately,” Pandey said.

SEBI chief also defended the new closing-price mechanism, saying it was introduced to enhance transparency in the market. He cautioned market participants against deliberately misusing the system or attempting to undermine confidence in it.

Pandey said the regulator’s surveillance capabilities under CAS are comparatively stronger, making it easier to identify unusual or manipulative activity than under the previous VWAP-based method.

The market regulator has introduced the new way to calculate the closing price of a stock, called the Closing Auction Session (CAS). It came into effect from August 3, 2026 replacing the current calculation process.

In the initial Phase, CAS will apply only to stocks in the Futures & Options (F&O) segment.

Under the new rule, instead of looking at trades over the last 30 minutes, CAS collects all buy and sell orders at the end of the day into a single pool and determines one price where the maximum number of shares can be traded.

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