The event on May 6, 2010, that caused a sudden temporary plunge across U.S. stock markets was the Flash Crash.
During the afternoon, major U.S. indexes dropped rapidly before recovering much of the loss. The Dow Jones Industrial Average briefly fell nearly 1,000 points, about 9%, within minutes. Some individual securities traded at extreme prices before normal conditions returned.
A large automated sell order by Waddell & Reed became central to investigations, while high-frequency trading and fragmented market structure amplified the move. Regulators concluded that no single factor fully explained every part of the event.
The U.S. Securities and Exchange Commission and the Commodity Futures Trading Commission later introduced measures including circuit breakers and improved controls for automated trading. The Flash Crash differed from a traditional prolonged bear market because its most dramatic movement happened within minutes and was partly reversed the same day.