The S&P 500 was the U.S. stock-market index that triggered a circuit breaker on March 9, 2020.
The S&P 500 fell 7 percent shortly after trading began, activating a Level 1 market-wide circuit breaker. Trading paused for 15 minutes, a safeguard designed to give investors time to reassess rapidly changing conditions.
The sell-off occurred amid the COVID-19 pandemic and an oil-price shock linked to a dispute between Saudi Arabia and Russia. U.S. markets experienced further circuit-breaker pauses on March 12, March 16, and March 18.
A circuit breaker is not the same as a permanent market closure or a price guarantee. It temporarily interrupts trading when predetermined thresholds are reached. The S&P 500 is a capitalization-weighted index of large U.S. companies, while the Dow tracks 30 major companies using a price-weighted method.