The S&P 500 entered a bear market in only 16 trading days during the COVID-19 stock-market crash.
From its record close on February 19, 2020, the index fell at least 20 percent by March 12, the fastest such descent from a record high in its history at that time. The decline reflected escalating concern about the coronavirus, business shutdowns, disrupted supply chains, and falling economic activity.
The Federal Reserve and governments introduced large monetary and fiscal responses. The S&P 500 reached its initial pandemic-era low on March 23, 2020, then rebounded strongly as vaccines, policy support, and expectations of economic reopening improved sentiment.
A bear market is commonly defined as a decline of at least 20 percent from a recent closing high. It is a market measurement, not a statement that every individual share fell by exactly the same amount.