SEBI's first CAS manipulation order flags Sensex spike on 13 August
Synopsis
Just ten days after India's Closing Auction Session went live, SEBI has alleged that two entities gamed the new mechanism on an expiry day — engineering three Sensex spikes in seconds to profit from linked derivatives. The regulator's first CAS order raises immediate questions about the structural vulnerability of the auction window.
Key Takeaways
SEBI issued its first interim order alleging manipulation in the Closing Auction Session (CAS) , which was introduced on 3 August .
The alleged manipulation occurred on 13 August , a weekly expiry day for Sensex derivative contracts.
Copthall Mauritius Investment Ltd allegedly drove three upward Sensex spikes — of 362.02 , 132.67 , and 405.08 points — through aggressive buy orders before cancelling them.
Mansi Share and Stock Broking Pvt Ltd allegedly placed sell orders worth ₹143.43 crore to push the Sensex downward, cancelling 99.06 per cent of them within seconds.
SEBI estimated wrongful gains of approximately ₹2.96 crore for Copthall and ₹71.65 lakh for Mansi.
The order is the first regulatory action testing the integrity of the new CAS mechanism on Indian exchanges.
The Securities and Exchange Board of India (SEBI) has issued its first interim order alleging manipulation of trades in the Closing Auction Session (CAS), targeting activity on 13 August 2025 — a weekly expiry day for Sensex derivative contracts. The regulator has named Copthall Mauritius Investment Ltd and Mansi Share and Stock Broking Pvt Ltd as noticees, alleging that coordinated cash-market orders were used to artificially move the Sensex and profit from linked derivatives positions.
What the Closing Auction Session Is
The Closing Auction Session was introduced on 3 August on Indian stock exchanges. It begins after normal cash-market trading closes at 3:15 pm, with a reference price established between 3:15 pm and 3:20 pm. An auction then runs from 3:20 pm to 3:30 pm to determine the final closing prices of eligible stocks. Because Sensex constituents can move sharply during this narrow window, such movements carry a direct bearing on the index's closing level and the settlement value of expiry-day options — making the session a potential target for manipulation, according to SEBI.
The Three Sensex Spikes
According to SEBI's order, the Sensex reference price on 13 August stood at 77,829.60, while the index eventually closed at 78,080. The regulator identified three sharp upward spikes during the auction period, alongside a broader downward movement.
In the first episode, the Sensex surged 362.02 points in approximately two seconds. A second spike lifted the index by 132.67 points in roughly 12 seconds, while a third episode saw a rise of 405.08 points in just 28 seconds. The speed and magnitude of these moves drew the regulator's attention.
What SEBI Alleged Against Copthall
SEBI alleged that Copthall Mauritius Investment Ltd was responsible for the upward pressure. The firm reportedly placed aggressive buy orders at the maximum permissible limit of 3 per cent above the reference price across Sensex constituent stocks. During the first spike, Copthall accounted for 99.91 per cent of total buy-order value, amounting to ₹66.57 crore. In the second episode, its share was 96.09 per cent of total buy orders worth ₹126.59 crore. In the third episode, Copthall placed buy orders worth ₹98.12 crore.
Critically, SEBI noted that Copthall cancelled its latest buy orders at 3:26:21 pm, suggesting the orders were not placed with a genuine intention to acquire the underlying shares — a key indicator of alleged spoofing behaviour.
What SEBI Alleged Against Mansi
Mansi Share and Stock Broking Pvt Ltd allegedly sought to push the Sensex in the opposite direction. According to the order, the broker placed sell orders for 12.65 lakh shares across eight Sensex constituents, totalling ₹143.43 crore, at prices substantially below the reference price. SEBI said 99.06 per cent of these sell orders were cancelled within seconds after the downward pressure on the index had been created.
Derivatives Link and Estimated Gains
SEBI connected the alleged cash-market activity to the derivatives positions held by both entities. Copthall reportedly held synthetic long positions through calls and puts at the 77,500, 78,000, and 78,500 strikes, while Mansi held net buy put positions at the 77,800, 77,900, and 78,000 strikes. Based on its assessment, SEBI estimated that Copthall allegedly made wrongful gains of around ₹2.96 crore, while Mansi allegedly gained ₹71.65 lakh from the activity.
The order marks the first regulatory test of the CAS mechanism and is likely to prompt closer surveillance of the auction window going forward.
Point of View
If proven, is textbook spoofing: flood the order book to move prices, then cancel before execution. What the order also reveals is a structural gap: a ten-minute auction window on expiry day, where index-constituent stocks are thinly traded and a single large participant can move the benchmark by hundreds of points in seconds, is an obvious target. The real question is whether the CAS design needs circuit-breaker safeguards specific to the auction phase, or whether surveillance alone can deter repeat attempts.
NationPress
20 Aug 2026
Frequently Asked Questions
What is SEBI's first Closing Auction Session manipulation order about?
SEBI has issued its first interim order alleging that two entities — Copthall Mauritius Investment Ltd and Mansi Share and Stock Broking Pvt Ltd — manipulated the Closing Auction Session on 13 August 2025, an expiry day for Sensex derivatives. The regulator alleged they used aggressive cash-market orders to artificially move the Sensex and profit from their derivatives positions.
What is the Closing Auction Session (CAS) and when was it introduced?
The Closing Auction Session is a price-discovery mechanism introduced on Indian stock exchanges from 3 August 2025. It runs from 3:20 pm to 3:30 pm after normal trading ends at 3:15 pm, and determines the official closing prices of eligible stocks, including Sensex constituents.
What did Copthall Mauritius Investment Ltd allegedly do?
Copthall allegedly placed aggressive buy orders at 3 per cent above the reference price across Sensex constituent stocks, accounting for up to 99.91 per cent of total buy-order value during individual spikes. It then cancelled those orders at 3:26:21 pm, which SEBI said indicated no genuine intent to buy the shares. SEBI estimated wrongful gains of approximately ₹2.96 crore.
What did Mansi Share and Stock Broking allegedly do?
Mansi allegedly placed sell orders for 12.65 lakh shares across eight Sensex constituents worth ₹143.43 crore at prices substantially below the reference price to push the index downward. SEBI said 99.06 per cent of these orders were cancelled within seconds. The regulator estimated Mansi made wrongful gains of ₹71.65 lakh.
How does the alleged manipulation connect to derivatives positions?
SEBI linked the cash-market activity to the entities' open derivatives positions. Copthall held synthetic long positions at the 77,500, 78,000, and 78,500 strikes, benefiting from an upward Sensex move. Mansi held net buy put positions at the 77,800, 77,900, and 78,000 strikes, benefiting from a downward move. The alleged cash-market orders were positioned to shift the Sensex in directions that would profit each entity's respective derivatives book.
