Explained: The reason behind Nifty's 200-point rally just before the closing bell

The NSE Nifty stunned Dalal Street on Monday by soaring nearly 200 points in the final minutes of trade despite the absence of any major trigger. The late-session spike, however, had little to do with fresh buying. Instead, it was the first visible impact of the Securities and Exchange Board of India's (Sebi) new Closing Auction Session (CAS) framework for F&O-eligible stocks.

At 3:15 pm, when regular trading came to an end, the Nifty was hovering around the 24,573 mark. Minutes later, however, the benchmark's official closing price was discovered at 24,774.30 through the closing auction, lifting its day's gain to 390.70 points, or 1.60%. The BSE Sensex, meanwhile, closed 544.39 points, or 0.70%, higher at 78,639.03.

The dramatic late-session jump was not the result of fresh buying after market hours but the first visible impact of Sebi's new auction-based closing price mechanism. The regulator has replaced the earlier 30-minute volume-weighted average price (VWAP) methodology with a call auction system for F&O stocks, fundamentally changing how official closing prices are determined.

Under the revised framework, continuous trading in F&O-linked stocks ends at 3:15 pm, followed by a 20-minute closing auction session during which buy and sell orders are aggregated and matched to arrive at a single equilibrium price. This auction-derived price now serves as the official closing price for F&O stocks and benchmark indices.

"The sharp late-session move in the Nifty reflects a system-driven concentration of liquidity rather than a sudden change in market sentiment," said Hariselvan Radhakrishnan, Founder & CEO of HST Wealth, a SEBI-registered research analyst firm.

According to him, the new framework allows prices to move within a ±3% band around a VWAP-based reference price. As large institutional orders get concentrated into a short auction window, heavyweight index constituents can witness sharp price adjustments, particularly when aggressive buying or short covering emerges.

"The move from around 24,589 to the 24,774 region reflects this concentration of liquidity and orders into the new auction structure, amplifying the end-of-day adjustment instead of a gradual intraday trend," he said. He added that the revised closing process makes the final few prints far more sensitive to institutional order flows than under the earlier VWAP-based methodology.

The new mechanism appeared to trigger significant buying interest in heavyweight financial and IT stocks during the auction, resulting in a sharp repricing that lifted the Nifty's official closing level well above its 3:15 pm reading.

From a technical perspective, the new closing methodology has also altered the chart structure.

Hitesh Rathi, Technical Analyst – Equity & Derivatives at Angel One, said the CAS-driven surge helped Nifty break decisively out of its nearly three-month consolidation range.

"The sharp upsurge witnessed in the final few minutes of trade, largely driven by the implementation of the new CAS-based settlement procedure, has signalled a decisive breakout from the preceding three-month trading range," Rathi said.

According to him, if the breakout sustains, the index could head towards its previous all-time high zone of 26,300-26,350, a view also supported by Point & Figure chart projections. However, he cautioned that the breakout is currently visible only on the cash index, while Nifty futures continue to face resistance around the 24,600 mark.

"This divergence between the cash and futures markets warrants caution. Confirmation across both segments would strengthen the validity of the breakout," he said, adding that investors should wait for more clarity as the market adjusts to the new settlement framework. He expects the 24,450-24,350 zone to act as immediate support, while 25,000-25,150 remains the next resistance band.

Rupak De, Senior Technical Analyst at LKP Securities, also urged caution despite Monday's strong finish.

"The index has rebounded after nearly two months of consolidation, delivering a decent recovery despite the prevailing subdued market sentiment. However, based on the closing price-adjusted chart, the index has rallied up to its 200-day moving average (200DMA), which is a crucial resistance level," he said.

According to De, the market now faces two possible paths. If the Nifty encounters resistance around the 200DMA, it could retrace towards the 24,400 level, allowing the recent rally to cool off. However, a sustained move above 24,800 would confirm a breakout above the long-term resistance and could trigger fresh buying, potentially extending the rally towards the 25,000-25,350 zone.