For any security if its derivative contracts crosses 95% of Market wide position limits (MWPL) then that security will be under ban for F&O.It means the combined open interest of all option and future contracts for all the months taken together for that particular underlying crosses 95% of MWPL.
Once a stock is under ban, one can trade in that particular contract only to offset his/her existing position but not allowed to open or add a new contract, simply saying one can not take a trade which increases open interest.
The stock comes out of ban only if its aggregated open interest comes down to 80% or below of MWPL.
MWPL is expressed in number of shares, it is lower of
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30 times average number of shares traded daily,during the previous calendar month,in the cash segment.
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20% of number of shares held by non promoters i.e 20% of the free float,in terms of number of shares of company.
Exchange release MWPL data for each stock traded in derivative segment on a monthly basis.