Which U.S. stock index briefly plunged nearly 1,000 points during the Flash Crash on May 6, 2010?

The U.S. stock index that briefly plunged nearly 1,000 points during the Flash Crash on May 6, 2010, was the Dow Jones Industrial Average. The drop was roughly 9 percent within minutes before much of it reversed.

The event began during an already difficult trading session, when markets were affected by concerns about the European sovereign-debt crisis. Selling accelerated rapidly across equities and other products. Some individual securities traded at bizarre prices, while several major indexes experienced exceptionally fast declines.

Investigations by U.S. regulators concluded that automated trading and a large sell order contributed to the episode. A trader, Navinder Singh Sarao, was later accused and convicted in connection with spoofing activity, although the event involved broader market conditions and multiple systems.

The Flash Crash differed from a traditional long-lasting bear market. Prices recovered quickly, and the Dow finished the day down 347.8 points rather than 1,000. Regulators later introduced safeguards such as circuit breakers and stricter controls for rapidly moving markets.