There has been a lot of discussion about the sharp closing moves since the new Closing Auction Session went live.

CAS itself is not a bad idea. Most large global markets have some form of closing auction. A large amount of institutional activity, especially from passive funds and other benchmark-tracking investors, happens near the close. Instead of the closing price being determined based on the average traded price during the final 30 minutes, CAS brings these orders together in an auction to discover one closing price.

The goal of CAS is to enable better price discovery and make it easier to execute large orders without moving prices abruptly. But the price dislocations we have seen over the last few days highlight some of the structural problems that are specific to the Indian markets.

Closing auctions work well when there is deep liquidity and a large and diverse ecosystem of market participants, including market makers and arbitrageurs. Whenever prices diverge between the cash market, futures, ETFs, or different exchanges, participants step in and arbitrage the differences away.

This ability to arbitrage is much more limited in India.

For one, it is impossible to express a short view in the cash market. We have a securities lending and borrowing mechanism, but it isn’t deep or easy enough to use. Unless borrowing stocks and shorting them becomes easy, there is bound to be structural upward pressure in the markets.

Then there is the difference in the cost of trading an option versus a futures contract. In April 2026, STT on futures was increased to 0.05% of the entire contract value, while STT on options is charged on the premium. So even though the STT rate on options is higher, trading futures is more expensive.

Once you add STT, exchange charges, spreads, and impact costs, the trading opportunity has to be quite attractive before a futures arbitrage trade is worth doing. The same directional view can often be expressed more cheaply through options. This leads to traders preferring options over futures.

India has over 13 crore registered investors, but only about 20–30 lakh traders trade actively on any given day. That’s it. We don’t have a large enough committed ecosystem providing two-sided liquidity across the cash market, futures, ETFs, and closing auctions.

CAS is not the reason for these structural limitations, but it makes them more apparent. The timing of its rollout is also unfortunate, because the RBI’s new norms on capital-market exposure, which limit banks’ exposure to capital-market activities, are going live at the same time.

When one instrument is more attractive than another, or when participants cannot express both bullish and bearish views easily, distortions are inevitable.

There might be tweaks required in how CAS itself works. But the larger issue of our markets being shallow is a complicated problem to solve. It requires building an ecosystem that encourages all kinds of traders and investors, with different time horizons, to participate easily.

Making shorting and securities lending easier, reducing distortions between instruments, and encouraging genuine market-making would be a good place to start.

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