On 9 March 2020, the S&P 500 triggered the first modern circuit breaker of the COVID-19 crash.
The index fell 7% from its previous close shortly after trading began, activating a Level 1 market-wide trading halt. Trading paused for 15 minutes under rules designed to give investors time to absorb rapidly changing information rather than continue selling in an uncontrolled rush.
The immediate shock combined fears about the new coronavirus with an oil-price dispute between Saudi Arabia and Russia. The S&P 500 had already entered a sharp decline after reaching a record closing high on 19 February 2020. The March halt was the first U.S. market-wide circuit breaker since the mechanism was introduced after the 1987 crash.
The word circuit breaker can cause confusion because individual stocks also have separate volatility pauses. The 9 March event applied to the broader U.S. market through the S&P 500 threshold. Similar market-wide halts were triggered again on 12 March, 16 March and 18 March 2020 as the crash intensified.