New Delhi, Aug. 29 -- Before Kevin Warsh said a word at Jackson Hole, the futures market had already placed its bet.

the instrument through which professional traders position overnight and in the pre-market hours - opened Friday's session pointing slightly lower, a tentative posture that hardened across the morning as speculation about the new Federal Reserve chair's first major policy address ran through trading desks. By early afternoon, after Warsh delivered remarks that were measurably more cautious on inflation than the market had priced, the futures curve had repriced quickly and the cash Nasdaq Composite closed down 0.52% at 26,402.42.

That sequence - pre-market caution, a speech that validated the caution, a session that sold o...