Market Insight

SEBI Bars Two Entities Over Alleged Manipulation of the New Closing Auction Session

• sebi
• cas
• closing auction session
• sensex
• bse
• market manipulation
• f&o regulation
• copthall mauritius investment
• mansi share and stock broking

Barely three weeks after India's new Closing Auction Session (CAS) mechanism went live, the market regulator has used it to catch — and act on — an alleged manipulation attempt. On August 19, 2026, the Securities and Exchange Board of India restrained Copthall Mauritius Investment and Mansi Share and Stock Broking from accessing the securities market, in connection with allegedly manipulative trading during the CAS window on the day of the Sensex expiry, August 13, 2026. The order came within six days of the alleged conduct — an unusually fast turnaround for a SEBI enforcement action.

What Is the Closing Auction Session, and Why Was It Introduced

CAS became effective on August 3, 2026. It's a 20-minute window, from 3:15 pm to 3:35 pm, that uses a call-auction mechanism to determine the closing price of a stock, rather than the older Volume Weighted Average Price (VWAP) method calculated over the last several minutes of continuous trading. For now, CAS applies only to stocks that are part of the futures and options segment, since their closing price directly decides how index and stock derivatives settle on expiry day.

The idea behind CAS is that an auction-based closing price is harder to nudge with a short burst of aggressive orders than a VWAP average — and easier for the regulator to scrutinise after the fact, since every order placed in that 20-minute window is time-stamped and auditable. SEBI's chairman had, in fact, spoken about exactly this at a capital markets conference just hours before the order was passed, cautioning that any attempt to manipulate CAS would draw swift action, and noting that the new system gives the regulator considerably more power to detect manipulation than the VWAP regime did.

This case is effectively the first real test of that claim.

What SEBI Says Happened on August 13

According to SEBI's interim order, both entities are alleged to have used large, well-timed orders in Sensex constituent stocks to influence the index's closing level — the Indicative Equilibrium Price, or IEP — for their own benefit, rather than trading based on genuine market views.

Copthall Mauritius Investment — a Mauritius-based entity that multiple reports identify as part of JPMorgan Chase's group structure — allegedly placed large, aggressive buy orders across Sensex constituent stocks at prices well above the prevailing reference price, in quick succession, pushing the IEP sharply upward. At the same time, Copthall held outstanding long call and short put positions on the index that stood to gain directly from exactly that kind of upward move. SEBI's order notes three sharp Sensex swings during the CAS window that day, each unfolding within a span of two to twenty-eight seconds — and that Copthall accounted for the overwhelming majority of buy-order value during the first of those spikes.

Mansi Share and Stock Broking, on the other hand, allegedly went the opposite way. It held open positions in expiry-day put options going into the CAS window, then placed aggressive sell orders across eight Sensex constituent stocks at prices well below the reference price — pushing the IEP down for a few minutes, in a way that benefited its existing put positions. SEBI's order notes that once those positions were closed out at the advantageous price, the sell orders were promptly cancelled.

SEBI says the immediate trigger for acting so quickly was that both entities had already built fresh positions in the following week's Sensex options — meaning any delay risked letting the same pattern repeat at the next expiry.

It's worth being precise here: SEBI's order reportedly states that the evidence does not, at this stage, indicate the two entities acted in concert with each other. These are two separate alleged schemes that happened to surface on the same expiry day, not a single coordinated operation.

The Penalty: Market Bans and ₹3.68 Crore Impounded

Under the interim order, SEBI has:

• Barred both entities from accessing the securities market

• Directed the impounding of ₹3.68 crore in alleged wrongful gains — ₹2.96 crore from Copthall Mauritius Investment and ₹71.65 lakh from Mansi Share and Stock Broking

• Barred both from placing, modifying, or cancelling any order during CAS in the equity segment until further notice (in Mansi's case, this restriction applies specifically to its proprietary trading account)

• Ordered their bank accounts frozen for any debit without SEBI's prior permission

This is an interim, ex-parte order — meaning it was passed without hearing the entities first, on grounds of market urgency — and SEBI has said a detailed investigation will follow before any final findings.

Why This Matters Beyond These Two Entities

Index expiry days already see outsized retail participation in options, and the closing price on those days determines exactly how those contracts settle — profit or loss, down to the last rupee. A manipulated closing level doesn't just affect the two entities allegedly involved; it can distort settlement values for every other position built around that same expiry, most of which belong to ordinary traders with no way of knowing the print was engineered.

Quick Answers

Who did SEBI bar, and why?

Copthall Mauritius Investment and Mansi Share and Stock Broking, over allegedly manipulative trading during the Closing Auction Session on the Sensex expiry day of August 13, 2026.

How much money did SEBI impound?

₹3.68 crore in total — ₹2.96 crore from Copthall Mauritius Investment and ₹71.65 lakh from Mansi Share and Stock Broking.

What is CAS, and when did it start?

The Closing Auction Session is a 20-minute, auction-based window (3:15–3:35 pm) that decides the closing price of F&O-segment stocks. It replaced the older VWAP method and became effective August 3, 2026.

Is this a final ruling?

No. It's an interim, ex-parte order. SEBI has said it will carry out a detailed investigation before reaching final conclusions.

Key Facts at a Glance

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