Circuit Breaker Stops Trades of Citigroup

An experimental circuit breaker for stock markets that was put in place after last month’s so-called flash crash kicked in for the second time on Tuesday after an erroneous trade caused a sudden plunge in the price of Citigroup shares.

Trading in the shares of Citigroup, one of the most heavily traded stocks in the United States, was paused for five minutes at 1:03 p.m. after an over-the-counter trade of about 8,821 shares was posted at a price of $3.3174, or 12.7 percent lower than the $3.80 price of the previous trade.

The trade was later canceled, according to Nancy A Condon, a spokeswoman for the Financial Industry Regulatory Authority, which regulates brokerage firms. Even so, Citigroup shares closed 5 percent lower for the day, at $3.79.

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