Sebi has passed an ex-parte interim order against Copthall Mauritius Investment Limited and Mansi Share and Stock Broking Private Limited for alleged manipulative trades during the closing auction session on BSE’s Sensex weekly expiry day. 67 crore of alleged wrongful gains and restrained both entities from accessing the securities market until the amount is deposited in fixed deposits marked with lien in favour of Sebi.

In the case of Mansi, the restraint applies to its proprietary trading account. The case relates to trading during the Closing Auction Session, or CAS, on August 13, 2026, a Sensex weekly options expiry day.

CAS was introduced by Sebi through a circular dated January 16, 2026 and became effective from August 3, 2026. Under the framework, normal trading in covered cash market stocks stops at 3:15 pm.

A reference price is then calculated between 3:15 pm and 3:20 pm. The auction runs from 3:20 pm to 3:30 pm, with random closure between 3:28 pm and 3:30 pm.

A single equilibrium price is discovered by 3:35 pm. Sebi said surveillance teams noticed abnormal spikes in the indicative equilibrium price of Sensex during the CAS on August 13.

96, rounded to 78,080 for calculations. The order said there were three sharp spikes in Sensex during the auction.

02 points in two seconds. 67 points.

08 points in 28 seconds. Sebi said Copthall was the dominant buyer during the auction.

6% of gross buy value in Sensex constituents during CAS. 91%.

Its 32 limit buy orders were placed across all Sensex stocks at nearly 3% above the reference price, while other market participants placed orders below 2%. Sebi said this showed an aggressive and index-wide price impact.

09%. 21% of the total buy order value.

Sebi said Copthall had expiry-day Sensex option positions that would benefit from a higher Sensex closing value. It held net buy call positions and net sell put positions at the 77,500, 78,000 and 78,500 strike prices.

The regulator said the cash market activity during CAS could not be viewed separately from its derivatives positions. Mansi, on the other hand, allegedly placed large sell orders at lower prices and then cancelled them.