SEBI flags prima facie manipulation in Sensex closing auction session, blocks two entities

SEBI has passed an ex-parte interim order against Copthall Mauritius Investment Limited and Mansi Share and Stock Broking Private Limited over prima facie manipulative trading during the Sensex Closing Auction Session (CAS) on August 13, 2026. The regulator said the trading patterns appeared linked to expiry-day Sensex options positions.

SEBI’s examination found three significant spikes in the Sensex Indicative Equilibrium Price (IEP) during the CAS on the BSE Sensex weekly expiry day. The first occurred between 15:20:41 and 15:20:43, when the Sensex rose 362.02 points from 77,661.40 to 78,023.42.

A second spike between 15:24:08 and 15:24:20 lifted the index by 132.67 points, while the third, between 15:25:49 and 15:26:17, resulted in a 405.08-point jump. SEBI noted that the movements occurred within periods ranging from two seconds to 28 seconds.

The regulator also observed a general downward trajectory in the Sensex between 15:21:03 and 15:26:00, which was interrupted by the sharp upward movements.

Copthall’s aggressive buy orders

According to SEBI, Copthall accounted for 86.6% of the gross buy value in Sensex constituents during the CAS, with gross purchases of ₹191.29 crore.

During the first spike, 88 buy orders worth around ₹66.64 crore were placed, of which Copthall accounted for approximately ₹66.58 crore, or 99.91%. Its 32 limit buy orders were placed at 3% above the reference price and spread across all Sensex constituents.

The pattern continued during the subsequent spikes. Copthall accounted for ₹126.59 crore, or 96.09%, of the buy-order value during the second spike and approximately ₹98.12 crore, or 85.21%, during the third.

SEBI said the large and aggressive orders appeared to influence the Sensex IEP and were connected to Copthall’s outstanding long call and short put positions.

Mansi’s sell orders

SEBI separately examined Mansi’s activity. Between 15:21:03 and 15:24:59, it placed aggressive sell orders across eight Sensex constituents, aggregating 12.65 lakh shares. Around 7.05 lakh shares were placed at prices 2.5% below the reference price. The entire 12.65 lakh shares were subsequently cancelled between 15:26:02 and 15:26:05.

SEBI said the activity appeared to suppress the Sensex IEP temporarily and benefit Mansi’s expiry-day put option positions.

Wrongful gains

SEBI estimated prima facie wrongful gains of ₹2.96 crore for Copthall and ₹71.65 lakh for Mansi, totalling ₹3.68 crore.

The regulator has ordered the amounts to be impounded, restrained the entities from accessing securities markets and prohibited them from participating in the equity CAS until further orders.

SEBI said protecting the integrity of CAS is critical because the closing price discovered through the mechanism is used for option settlement and mutual fund NAV determination. It also said the new CAS framework gives the regulator greater ability to identify potential manipulation compared with the earlier VWAP system.