The emergency market-wide trading halt first triggered in the United States on 9 March 2020 was a circuit breaker.
U.S. market circuit breakers are automatic mechanisms designed to pause trading after unusually large declines. The first level is tied to a percentage fall in the S&P 500 from the previous close. The pause gives investors time to process information and can reduce disorderly selling.
The 9 March 2020 halt occurred after the S&P 500 fell 7% shortly after trading began. Additional U.S. halts followed on 12, 16, and 18 March as the COVID-19 pandemic intensified economic uncertainty and market volatility.
Circuit breakers do not prevent losses or guarantee a recovery. They temporarily interrupt trading under defined conditions. The 2020 halts are sometimes confused with the 1987 crash, which led to the creation of modern U.S. market-wide circuit-breaker rules.