Comment by wmchen

It fell by exactly 20.00% because it hit the NSE's lower circuit, which prevents trades below that price for the rest of the session without technically halting trading. This is effectively a trading halt because there are presumably no buy orders at the asking price, and the real value of the asset is likely much lower. [1]

[1]: https://www.nseindia.com/static/products-services/equity-mar...