Which emergency market mechanism was first triggered in the United States on March 9, 2020?

A circuit breaker was first triggered in the United States on March 9, 2020, during the market crash linked to the COVID-19 pandemic and an oil-price shock.

The S&P 500 fell 7% from its previous close shortly after trading began, activating a Level 1 market-wide circuit breaker. Trading paused for 15 minutes, giving participants time to process orders and information before reopening.

Modern U.S. circuit breakers were introduced after the 1987 crash and later redesigned. The Level 1 threshold is reached after a 7% decline, Level 2 after a 13% decline, and Level 3 after a 20% decline, all measured against the prior closing value.

A circuit breaker pauses trading; it does not guarantee that prices will recover. On March 9, the mechanism limited immediate trading activity, but markets remained highly volatile during the weeks that followed.