Adani group stocks, Nifty Bank, Small Cap and Midcap stocks are continuously falling since many days.
Retail investors are constantly losing their money due to constant downsides of the stock market.

Here there are 3 key reasons
(1) FII has been constantly selling for many days: This is one of the major reasons why the market is down today.
FII is the key factor of how the market will behave, but, FII has been on a rampant mode and creates a selling pressure which leads to market falls heavily.
Mid cap and small cap index performed poorly because of poor results from listed stocks on BSE and NSE.
FII has been selling because they are not getting any return on their investment so they are diverting their funds to other countries where they can get absolute return on their investment.

(2) Adani stocks are in pressure: Today adani stocks are in heavy pressure after the US Securities and Exchange Commission has asked a US court for permission to personally email summons to billionaire Gautam Adani and group executive Sagar Adani over alleged fraud.

(3) Quarterly earnings: Q3 results have impacted stock market as most of the companies q3 results are not up to the mark and below from their estimation which create heavy selling pressure on market.
Along with adani group shares, Paytm, ICICI bank and HCL technologies are also one of the major reasons for the heavy crash in the market.
This quarter has been challenged in many ways as FII is constantly selling, Results are not as per estimation, trump effect and global clue not in favour.
Above are the main reasons for falling markets today.