The S&P 500 triggered U.S. market-wide circuit breakers four times during the COVID-19 stock-market crash of March 2020.
The four halts occurred on March 9, March 12, March 16, and March 18, 2020. Each followed a sufficiently large intraday fall under rules designed to pause trading and give investors time to absorb rapidly changing information. The shutdowns were a striking feature of the crash.
The decline reflected fear that the coronavirus pandemic would halt economic activity, disrupt supply chains, reduce earnings, and create widespread unemployment. An oil-price dispute between Saudi Arabia and Russia added further pressure in early March. Central banks and governments responded with emergency measures, including interest-rate cuts, lending programs, fiscal support, and public-health restrictions.
The S&P 500 fell about 34% from its February 2020 peak to its March 23 low, then rebounded rapidly. The circuit breakers did not prevent losses; they were designed to slow disorderly trading. They are often confused with individual-stock halts, which can apply under different rules.