Sensex and Nifty steep sell-off on Oct 21: what is known so far

1. What happened

   According to a TradingView headline, India's benchmark Sensex and Nifty indices saw a steep sell-off, described as a stock market crash. The article's details on the scale of the fall were not available in the provided material.

2. When it started

   The sell-off is reported to have taken place on October 21. The year is not stated in the material provided.

3. How it spread

   This explainer relies only on a single headline from TradingView, accessed through a Google News link. The article's body text, index levels and percentage moves could not be verified.

4. Why it matters

   The headline says key factors drove the sell-off, but those factors are not described in the material provided. Readers should check the original article or reports from major financial outlets for the causes.