Day Traders Call For A One-Day Boycott Against CAS On August 12

Retail traders have called for a one-day boycott of trading on the stock market on August 12, 2026 to protest the recently introduced Closing Auction Session (CAS), saying the new mechanism puts them at a disadvantage and could create uncertainty around the market close.

Several traders have taken to social media platform X (formerly Twitter) to back the proposed protest, with some calling on the trading community to avoid taking even a single trade on August 12. Traders have also raised concerns over frequent changes in market rules and high securities transaction tax (STT) on trading.

An X account, @Mohitsharma202, which has 94,900 followers, said trading is his profession and livelihood and urged traders to support the movement. “If you’re a trader, I request you to avoid taking even a single trade on 12th August 2026,” he wrote in his post.

Another trader, Ravindra Elicherla, who uses the username @Ravindra_PE and has 19,800 followers, criticised the lack of visibility during the auction period. “At 3:15 pm, every retail trader walks into a blind window — a black box with no visibility into what price will print at 3:30. Big institutions face no such blindfold. With enough capital, a handful of options or futures orders can tilt where that final price lands. Manipulation in Indian markets isn’t new — every experienced trader already knows the game. What CAS does is hand the players with the deepest pockets a mechanism where the retail crowd is structurally blind for the final 15 minutes, and call it fairness,” said Elicherla.

“I think it's time for the trading community to do a Jantar Mantar,” another X user, @prafulkulkarn18, who has 59,700 followers, posted.

Traders Seek Change In Weekly Expiry Timing

The concerns are not limited to the auction mechanism itself. A three-day-old X account, @IRITA_India, representing Indian Retail Investors & Traders Association (IRITA), has called for weekly expiry contracts to be delinked from CAS. IRITA said it is not against CAS but wants weekly expiry contracts to continue expiring at 3:15 PM, as was the established practice. “Weekly expiry contracts being linked to CAS can create unintended distortions and uncertainty during the crucial final minutes of trading,” IRITA said in a post.

The association said moving weekly expiries to 3:15 pm could reduce unintended price distortions, improve market predictability and make expiry-day trading smoother for retail participants. IRITA described the proposal as a “simple, practical and constructive solution” that would allow the transition to CAS without affecting its broader objective.

The association has urged the Securities and Exchange Board of India (Sebi) and the stock exchanges to consider the change and hear the concerns of market participants.

Why Traders Are Opposing CAS

Traders have also alleged that the new mechanism has resulted in differences between the closing prices of stocks and a wider divergence between the Nifty and the Sensex. Some traders claim these differences have resulted in significant losses, particularly for those holding positions close to market close.

Sebi introduced CAS on August 3 for around 200 stocks that are also traded in the derivatives segment. The closing price for stocks in the equity cash market was previously determined using the Volume Weighted Average Price (VWAP) of trades executed during the final 30 minutes of the Continuous Trading Session (CTS). Under CAS, orders are brought together during the closing auction to discover a single closing price. The change is intended to address some of the problems associated with the earlier VWAP-based system.

What Sebi Says About The New System

Sebi introduced after receiving feedback from global passive fund managers that Indian equities often see significantly higher volatility towards the end of the trading day compared with other major markets. According to Sebi, volatility around the close can affect the performance of mutual funds, passive funds and exchange-traded funds (ETFs). Sebi said it could also create differences between the price at which different investors execute their trades and affect index tracking.

The regulator said the previous VWAP-based closing mechanism could see large institutional trades near the end of the session with a disproportionate impact on prices. Volatility could also increase on days involving index rebalancing and derivatives expiry, potentially creating distortions for passive funds and arbitrage strategies.

Sebi’s research and its review of practices in other major markets found that a closing auction can result in a more stable closing price than a VWAP-based mechanism.

In its consultation paper, Sebi had also noted that closing auctions were already in use across major markets in the US, Europe and Asia. It said the system brought liquidity into a single auction and gave different categories of investors an equal opportunity to participate in price discovery.

For retail traders, the new system has become a major concern. The planned August 12 boycott and calls to change the weekly expiry timing show that traders want more clarity and certainty in the final minutes of trading.