A circuit breaker halted US stock trading during the 2020 market crash when the S&P 500 fell 7%.
On March 9, 2020, the S&P 500 dropped 7% shortly after the opening bell, activating a Level 1 market-wide circuit breaker. Trading paused for 15 minutes under rules designed to give investors time to absorb extraordinary price movements and reduce panic-driven orders.
The same safeguard was triggered again on March 12 and March 16, as the COVID-19 pandemic and an oil-price dispute intensified market fear. These pauses do not permanently stop a decline; they temporarily interrupt trading under specified thresholds. They are also different from individual-stock limit rules, which apply to one security rather than the entire US market.