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New stock option closing auction rules raise delivery risk for short sellers
For the first monthly test of the mechanism, NSE and BSE expiries fall on 25 August and 27 August, with delivery obligations only becoming clear after the auction order window ends.
LiveMint Markets reports that newly introduced closing auction rules are creating uncertainty for stock option traders, especially short sellers with multiple positions or combination strategies. The concern is that late-session volatility in the order-matching window can move options from out of the money to in the money, meaning traders may not know they have stock delivery obligations until settlement concludes.
According to LiveMint Markets, stock delivery is triggered only when a stock option expires in the money, so participants will not know whether they must take or deliver underlying shares until the auction finishes. Options that end out of the money expire worthless and do not trigger delivery obligations.
The outlet notes that index derivatives are unaffected because index contracts settle strictly in cash. LiveMint Markets also highlights that traders caught short on underlying shares during an unexpected in-the-money assignment may face higher premiums the next day.
LiveMint Markets further details the new timetable: continuous trading ends at 3:15 pm, then no orders can be placed for five minutes as the market transitions to the closing auction. Between 3:20 pm and 3:30 pm, orders can be entered within a plus or minus 3% band around a reference price, and the exchange randomly closes the window between 3:28 pm and 3:30 pm, publishing the official closing price at 3:35 pm. The upcoming monthly stock option expiries on 25 August for NSE and 27 August for BSE are positioned as the first key test of the mechanism.