U.S. stock exchanges triggered market-wide circuit breakers four times in March 2020.
The halts occurred on March 9, March 12, March 16, and March 18, 2020, during the market shock associated with the COVID-19 pandemic and the collapse in oil prices. Each halt followed a fall of at least 7 percent in the S&P 500 before 3:25 p.m. Eastern Time, under the Level 1 threshold then in force.
Circuit breakers pause trading to give investors time to process information and reduce disorderly selling. The March 2020 sequence was unusual because four market-wide halts occurred in a single month. It showed how quickly fear could move through highly connected global markets.
These halts should not be confused with ordinary pauses in individual stocks or with the intraday trading interruption during the 2010 Flash Crash. The March 2020 measures were market-wide and applied to the U.S. equity market under rules adopted after earlier crashes.