A circuit breaker was triggered four times during the March 2020 U.S. stock-market crash.
Circuit breakers are automatic trading pauses intended to slow panic and give investors time to assess rapidly changing information. In March 2020, U.S. market-wide Level 1 halts were triggered on 9 March, 12 March, 16 March, and 18 March as the COVID-19 shock and an oil-price dispute produced extreme selling.
The mechanism was introduced after the 1987 Black Monday crash. Modern U.S. rules pause trading when the S&P 500 falls 7 percent or 13 percent from the previous close; a 20 percent fall ends trading for the day. These thresholds are calculated from the prior session’s close.
A circuit breaker is not the same as a company-specific trading halt. Market-wide breakers apply across U.S. equity markets, while individual securities can be paused for news, unusual volatility, or regulatory reasons. The March 2020 pauses did not prevent the broader bear market, but they were designed to reduce disorderly trading.