The Sensex remained relatively calm during Friday's closing auction, one day after a 2,000-point plunge during the monthly derivatives expiry raised fresh concerns about the newly introduced CAS (Closing Auction Session).

According to experts, Friday's subdued close suggests that Thursday's sharp swings were likely an expiry-driven anomaly rather than evidence of a persistent problem with the new closing-price mechanism.

Thursday's move had rattled traders in particular because it occurred during the first monthly derivatives expiry after the introduction of CAS, and market participants noted that the expiry itself amplified the magnitude of the move.

The CAS is a dedicated closing auction window introduced by Indian exchanges to determine closing prices more transparently, replacing the earlier system in which closing prices were derived largely from the weighted average of trades in the final minutes of the session. Because closing prices serve as benchmarks for derivative settlement, index funds, and mark-to-market valuations, any unusual move during the closing auction draws heightened scrutiny.

Monthly derivatives expiries are themselves known for elevated volatility, as large open positions in index futures and options are unwound or rolled over, often producing outsized swings in the final minutes of trade. That backdrop is why experts view a calm close on a non-expiry day like Friday as a more meaningful indicator of how the new mechanism behaves under normal conditions.

Market participants are expected to keep watching closing auctions over the coming sessions, particularly at the next derivatives expiry, to gauge whether the CAS consistently produces orderly closes.

Source: Economic Times Markets