India's Sensex Suffers Another Flash Crash During Closing Auction, Plunging Nearly 3% Intraday
nashnova research
India's Sensex plunged as much as 2.9% during the closing auction on August 27 after a heavyweight stock was hit by limit-down orders — the newly launched mechanism's liquidity weakness is now fully exposed, and next week's MSCI rebalance will be an even bigger test.
What happened in the final minutes?
Sensex stood at 77,182.91 when continuous trading ended at 3:15 pm, then plunged to 74,983.19 during the closing auction — a 2.9% drop.
This means → roughly 2,200 points evaporated in a matter of minutes, though most of the loss was recovered before the final print; the index closed down 0.7% on the day.
Tejas Shah, head of derivatives at Equirus Securities, pointed to a single index heavyweight that was hit by sell orders pegged at the 3% limit-down price during the auction window.
What happened in the derivatives market?
The 75,000-strike put option expiring that day spiked 4,800% during the auction, then gave back all gains before the close.
Puts at 76,000 and 75,500 strikes showed similarly extreme swings.
In plain terms = someone hammered the index down during the auction, making the matching puts briefly worth a fortune — but once the closing price snapped back, that windfall vanished. The whole episode looked like a violent price pulse.
Why is this closing-auction mechanism so controversial?
India introduced a closing auction — a mechanism that determines the final price through concentrated bidding in the last minutes — earlier this month, covering over 200 stocks. The goal: align with global practice and curb price manipulation.
Since launch, the mechanism has repeatedly triggered unexplained sharp swings in benchmark indices, prompting India's Securities and Exchange Board (SEBI) to investigate suspected manipulation.
Earlier this month SEBI named Copthall Mauritius Investment (a J.P. Morgan subsidiary) and local broker Mansi Share and Stock Broking, alleging they manipulated the Sensex closing price on August 13 to profit from derivatives positions.
How do participants and regulators see it?
Suniil D. Pachisia, vice president at Pratibhuti Viniyog, called teething problems expected but said "it is increasingly difficult to judge price moves inside the auction window." He labeled this latest episode "yet another textbook case."
SEBI Chairman Tuhin Kanta Pandey said after the close that regulators are not considering any changes to the mechanism, describing the system as functioning normally and expecting participation to rise over time.
This reflects a widening gap between the regulator's confidence and the market's lived experience — one side says the system works, the other keeps getting blindsided by flash crashes.
Where is the next stress test?
Next Monday's MSCI month-end index rebalance will be the biggest liquidity test the new mechanism has faced since launch.
MSCI's August review changes take effect at that day's close; passive funds and ETFs tracking MSCI benchmarks must adjust holdings inside the closing auction window. This means → a large wave of passive money will funnel into a window already proven to be thinly traded.
Shah warned: "Given what we've seen, it's best not to hold naked derivatives positions heading into the auction." Whether the MSCI rebalance passes smoothly will determine if this mechanism can win back market confidence.
市场有风险，内容仅供研究参考，不构成投资建议。