What emergency trading measure was triggered four times during the U.S. stock-market crash of March 2020?

A market-wide circuit breaker was triggered four times during the U.S. stock-market crash of March 2020.

The circuit breakers halted trading after severe intraday declines as investors reacted to the COVID-19 pandemic, economic shutdowns, and an oil-price dispute. The four halts occurred on 9, 12, 16, and 18 March 2020.

Under the rules then in force, a Level 1 halt followed a 7% fall in the S&P 500 before 3:25 p.m. Eastern Time. A 13% fall could trigger a second halt, while a 20% decline ended trading for the day. The system is designed to give investors time to assess rapidly changing information.

These halts did not permanently prevent losses and were not the same as a trading suspension of one individual company. The 2020 crash was also unusually fast, but markets later recovered as fiscal, monetary, and public-health responses changed expectations.