What emergency trading rule was triggered for the first time on March 9, 2020, during the U.S. stock-market crash?

A Level 1 market-wide circuit breaker was triggered for the first time on March 9, 2020, during the U.S. stock-market crash.

The S&P 500 fell at least 7 percent shortly after trading opened, activating a 15-minute trading halt on U.S. stock exchanges. The halt was designed to give investors time to absorb information and reduce the risk of disorderly, feedback-driven selling.

The March 2020 crash reflected the economic shock of the COVID-19 pandemic, uncertainty about business closures, and an oil-price dispute between Saudi Arabia and Russia. Additional U.S. market-wide halts occurred on March 12 and March 16 as prices continued to fall.

Circuit breakers do not prevent losses or guarantee that prices will recover. They pause trading when preset thresholds are reached. The U.S. system was created after the 1987 crash and later revised, including changes adopted after the 2010 Flash Crash.