Yesterday, Citigroup stock was halted for 5 minutes due to the new circuit breakers being triggered.  Most reports in the press today quote market participants as saying this was a good thing and the system worked.  But did it really? What caused the breaker to be triggered?  One trade of 8820 shares at a price $3.3174.  Think about that, one trade triggered a 5 minute halt in a stock that trades almost 1 billion shares on a daily basis.  The “trade” now appears to be a keypunch error.  Most likely a VWAP trade that was printed on a TRF (trade reporting facility). Being the posterboy for HFT liquidity rebate traders, Citigroup always has a deep volume of bids and offers so the probability of this being a real trade was almost zero.

A circuit breaker should not be triggered for just one trade.  We recommend that there should at least be a minimum number of trades before the breaker is triggered.  This would prevent false triggers from going off. 

One other point:  Every trader in the world who has the ability to print a trade on an exchange or TRF now has the power to halt a stock at any given time.  There seems to us to be a high probability of  an abuse of power here.  If the circuit breakers get extended to all stocks, you can expect to hear the  popping of breakers more frequently than popcorn popping in  a microwave.