Wednesday's sell-off began after the government's report that retail sales plunged in September by 1.2 percent — almost double the 0.7 percent analysts expected — made it clear that consumers are reluctant to spend amid a shaky economy and a punishing stock market.
Selling accelerated in the last hour of trading, a common occurrence during the eight days of heavy declines. One reason for the heavy selling: Mutual funds need to unload stock to pay investors who are bailing out of the market.