What market-wide safeguard first halted U.S. trading during the COVID-19 stock-market crash?

Circuit breakers first halted U.S. trading during the COVID-19 stock-market crash.

On March 9, 2020, the S&P 500 fell 7% shortly after the opening bell, activating the market’s Level 1 circuit breaker. Trading paused for 15 minutes under rules designed to give investors time to assess rapidly changing conditions.

Further U.S. circuit-breaker halts occurred on March 12, March 16, and March 18 as the pandemic intensified and markets reacted to travel restrictions, economic shutdowns, and emergency policy measures. The rules apply to broad U.S. equity indexes rather than just one individual stock.

Circuit breakers do not prevent losses or guarantee a recovery. They temporarily interrupt trading when predetermined percentage thresholds are reached. The system was developed after earlier market shocks, especially the 1987 crash.