Which U.S. stock index fell about 9% during the Flash Crash on 6 May 2010?

The Dow Jones Industrial Average fell about 9% during the Flash Crash on 6 May 2010. Much of that decline occurred within minutes before the market rapidly recovered some losses.

The event affected several major U.S. indexes and thousands of individual securities. A large sell order, algorithmic trading and reduced market liquidity interacted in ways that amplified price movements. Some trades were executed at extremely unusual prices before being canceled or adjusted under exchange rules.

Investigations by U.S. regulators concluded that a large automated sale of E-mini S&P 500 futures helped trigger the rapid market movement. The crash demonstrated how electronic trading systems could transmit pressure across markets at extraordinary speed.

The Dow was not the only index involved, but its widely reported intraday fall made it a common reference point. The 2010 Flash Crash was a brief trading disruption, unlike the multi-year declines associated with the 1929 crash or the dot-com collapse.