From Bloomberg:
By one metric, investors would have to go back 75 years to find the last time the S&P 500’s losses were this abrupt.
Bespoke Investment Group observed that the S&P 500 has closed more than four standard deviations below its 50-day moving average for the third consecutive session. That’s only the second time this has happened in the history of the index. May 15, 1940, marked the end of the last three-session period in which this occurred: