Foreign portfolio investors (FPIs) emerged as heavy sellers in Indian equities on Friday, pulling out a net Rs 20,637 crore in a single session, recording one of the sharpest single-day selloffs in recent years, as markets grappled with the impact of the latest MSCI index rebalancing.Before this, the sharpest fall occurred last month (April 2, 2026), when FIIs pulled out Rs 19,837 crore in a single day, data from ACE Equity showed.The selloff came as benchmark indices fell 1.5%, with market participants attributing much of the late-session weakness to passive fund flows linked to the index reshuffle. The scale of foreign investor activity stood out not just because of the outflow figure, but also because of the sheer volume traded during the session.FPIs accounted for Rs 198,465 crore of trading activity out of the NSE's total turnover of Rs 287,452 crore, representing nearly 69% of the day's traded value, provisional data on the NSE showed.Despite ending the day as net sellers of Rs 20,637 crore, FPIs traded nearly 9.6 times that amount during the session. In comparison, domestic institutional investors (DIIs) were net buyers of Rs 16,260 crore and recorded total trades worth Rs 53,772 crore, or around 3.3 times their net purchase value.The high participation prompted questions over whether the activity was solely driven by MSCI-related portfolio adjustments or whether high-frequency trading (HFT) strategies amplified volumes around the index rebalance. The size of the turnover also sparked debate over how much of the reported foreign outflow reflected actual portfolio repositioning and how much may have been linked to short-term trading activity.Nilesh Shah, MD of Kotak Mahindra Asset Management, questioned whether the surge in activity was surprising given that Indian equities are currently not a key focus area for FPIs. He also asked whether Friday's volumes were driven purely by MSCI rebalancing or whether high-frequency trading (HFT) activity around the index reshuffle had amplified turnover. Shah further wondered how much of the reported net FPI outflow of Rs 20,637 crore could be attributed to HFT trades.Market expert Gurmeet Chadha also questioned the sharp rise in trading volumes, arguing that ‘speed and money muscle’ were being used to distort market moves. He further highlighted the addition of 31,000 short contracts even as Brent crude hovered around $90 a barrel and hopes of a weekend deal persisted. Calling the activity suspicious, he said ‘we need to act and trap this cartel’.According to Abhilash Pagaria, Head of Alternative and Quantitative Research at NuvamaWealth, the rebalancing led to outflows of around Rs 8,000-8,500 crore. He said the figure was somewhat higher than in previous reviews due to free-float adjustments in stocks such as Bajaj Finance, HUL and TCS, among others, describing the impact as a one-time adjustment arising from a new methodology.MSCI RejigMSCI's latest review saw Federal Bank, MCX, NALCO and Indian Bank added to the MSCI Standard Index, while Hyundai Motor India, Jubilant FoodWorks, Kalyan Jewellers and RVNL were removed. The changes took effect at the close of trade on May 29.The review also resulted in weight increases for Adani Power, BPCL, Nykaa, Trent and OFFS. Despite the reshuffle, India's overall weight in the MSCI Standard Index remained broadly stable at around 12.3%, compared with 12.4% earlier. The total number of Indian constituents in the index also remained unchanged at 165.Beyond the Standard Index, MSCI announced a broader rejig of its Small Cap Index. According to Nuvama, more than a dozen Indian stocks were excluded, reducing the India stock count to 459 from 474. New additions included IREDA, Anthem Biosciences, Fractal Analytics, Pine Labs and Emmvee Photovoltaic, while Cello World, Redtape, Raymond Lifestyle, Indigo Paints, Balu Forge and Blue Jet Healthcare were among the exclusions.Index review days typically witness elevated volumes as passive funds tracking MSCI benchmarks adjust their holdings to match the revised composition.(Disclaimer: Recommendations, suggestions, views and opinions given by the experts are their own. These do not represent the views of The Economic Times)