Any scrip trading in F&O segment will have a limit set. So the scrip will be banned only when open interest has reached 95% of the Market wide position limit on any trading day.
Once the open position goes below 80% of the mentioned number trading will resume (new positions can be taken), till then only position holders can trade (square off the positions).
You can find the details in the link below.
http://www.nseindia.com/products/content/derivatives/equities/sec_ban.htm
