Citadel Securities, SEC Battle Over Microseconds in IEX Case (1)

A federal judge challenged a lawyer for Citadel Securities LLC about its efforts to thwart a new kind of market order from IEX Group Inc., the stock exchange operator made famous by “Flash Boys.”

“It’s you who’s going to a federal agency and saying stop a private entity from doing what they want to do,” U.S. Circuit Judge Justin Walker said at a hearing in Washington on Monday, after attorney Jeffrey Wall argued that the order type interferes with the natural course of the market.

The order type, known as D-Limit, has a roughly 350-microsecond delay to blunt ...