New Delhi, Dec. 8 -- The first day of the new futures and options (F&O) pre-opening session on Monday drew mixed reactions, with many stakeholders welcoming the move while brokers raising concerns about a sudden, unexpected rule change.

open session was to begin, the National Stock Exchange (NSE) issued a circular informing brokers that client margins would be blocked before trades are executed during the 9:00-9:08 am window. This is very different from the transaction rules for the normal market hours of 9:15 am-3:30 pm.

In normal trading, a trade is executed first and then the margin is blocked. But NSE informed brokers late Friday that this rule would be reversed for the F&O pre-open, which one discount broker described as a "bolt ou...