Black Wednesday was the 1992 United Kingdom market event that forced the pound sterling out of the European Exchange Rate Mechanism.
On September 16, 1992, the British government tried to keep sterling within the ERM’s permitted exchange-rate band. Heavy selling pressure made that increasingly difficult. The government raised interest rates twice during the day, eventually announcing a rise from 10 percent to 15 percent, but the measures failed to restore confidence.
Later that day, Chancellor of the Exchequer Norman Lamont announced that the United Kingdom would suspend sterling’s ERM membership. The event became known as Black Wednesday. The immediate financial loss damaged the reputation of Prime Minister John Major’s government, although the economy later recovered outside the ERM.
George Soros is often associated with the episode because his Quantum Fund reportedly made a large profit by betting against the pound. However, the answer to this question is the event’s name, not the name of the trader. Black Wednesday concerns a currency crisis rather than a conventional share-price crash.