SEBI Examines August 3-4 Trades for Possible Manipulation Under New Closing Auction System

The Securities and Exchange Board of India (SEBI) is examining trading activity recorded during the first two days of India’s newly introduced Closing Auction Session (CAS), with particular attention on transactions executed on August 3 and 4. The regulator is assessing whether unusual movements in index levels during the auction period were driven by normal market activity or whether certain trades may have been intended to influence closing prices.

The scrutiny follows significant movements in the Nifty during the final minutes of trading on the first two days of the new mechanism. According to people familiar with the matter, SEBI has obtained trading information from the stock exchanges and is studying the data to understand what drove the sharp changes observed around the transition into the closing auction.

Regulator seeks detailed trading data

SEBI's examination began after concerns emerged over the difference between index levels before the Closing Auction Session and the levels recorded after the auction concluded.

The regulator has requested relevant trading data from the exchanges covering the initial two days of CAS. The exchanges have supplied the information, and SEBI is now analysing individual trading activity and price movements.

The objective is not simply to identify trades that moved the market. Instead, the regulator is looking at whether trading patterns indicate an attempt by market participants to deliberately affect the closing price.

On August 3, the Nifty was trading near 24,573 around 3:28 pm before reaching approximately 24,774 by 3:30 pm. That represented a move of roughly 201 points in the final minutes of the session.

A similar pattern was seen the following day. On August 4, the index was around 24,463 at 3 pm and rose to approximately 24,615 by 3:15 pm, a gain of about 152 points.

These movements attracted attention because they occurred during the early implementation of the new closing mechanism.

Why the Closing Auction Session matters

CAS was introduced to change the way official closing prices are established for eligible securities. The auction operates for 15 minutes, from 3:15 pm to 3:30 pm, during which buy and sell orders are collected and matched at a price designed to maximise the volume of trades.

The system was introduced with the broader objective of improving price discovery and making closing prices more representative of market conditions. It is also intended to reduce the possibility of price manipulation around the market close and bring India's market structure closer to practices used in other major markets.

However, the unusual movements during the first two sessions have raised questions about how the mechanism behaves when participation and liquidity are limited.

Liquidity could be an important factor

Market participants have pointed to relatively weak liquidity during the auction window as one factor that could potentially increase the sensitivity of certain stocks or indices to large orders.

The concern is particularly relevant where cash-market turnover is low. A sufficiently large transaction, or a series of coordinated transactions, could have a greater effect on prices in such circumstances than it would in a deeper market.

One possible scenario discussed by market participants involves an investor taking a substantial position in a passive index product while simultaneously holding positions linked to the same index. If buying activity in the cash market were to push the underlying index higher, the resulting movement could potentially benefit a related position.

Such possibilities may become more important on expiry days, when positioning in derivatives markets can be particularly significant and cash-market liquidity may be comparatively limited.

However, an unusual or influential trade does not automatically amount to market manipulation.

Proving manipulation may be challenging

For SEBI to establish that manipulation occurred, simply showing that particular trades affected an index or closing price may not be sufficient.

The regulator would need to determine whether there was an intention to influence the market and whether multiple transactions were coordinated for that purpose. Distinguishing legitimate trading strategies from deliberate attempts to distort prices can therefore be a complex part of the investigation.

SEBI's current review is consequently focused on understanding the broader trading pattern rather than drawing conclusions from individual transactions alone.

Sources indicated that the regulator's monitoring is intended to protect orderly market functioning while allowing genuine market participants to continue trading normally.

SEBI continues to monitor CAS rollout

Alongside its examination of the August 3 and 4 trades, SEBI has been monitoring the broader implementation of CAS. The regulator has also asked brokers to improve investor awareness about the new system and make indicative auction prices more visible on their trading platforms.

The changes are aimed at helping investors understand how prices can behave during the auction and reducing confusion around the new closing process.

For now, the examination of the first two days represents an early assessment of how the mechanism functioned in actual market conditions. Whether the unusual index movements were simply a consequence of the new auction structure, liquidity conditions and trading behaviour—or whether they reveal deliberate attempts to influence prices—will depend on SEBI's analysis of the underlying data.

The regulator's review therefore remains an important test for the newly introduced Closing Auction Session and its ability to deliver orderly and credible price discovery at the end of the trading day.