Why did the Nifty and the Sensex correct so sharply from higher levels on 15 April?
Answer 
Sensex and Nifty were extremely strong in the first half but reversed gains to end in the red after a sharp fall in European markets and also in US futures. The economic implications of the lockdown extension also weighed on sentiments. On a closing basis, the Sensex closed 310 points lower at 30,380, while Nifty fell 69 points to close at 8,925. Volatility index (VIX) fell below 50 after a long gap. While the fall may not appear to be steep, the real story of the day was the intraday fall. Sensex lost nearly 1200 points from its intraday peak while the Nifty dropped 350 points from the peak. The big sector leading the markets down was of course, banking. Kotak Mahindra Bank and HDFC Bank were the top losers in the index, shedding 6.23 per cent and 3.57 per cent, respectively.
The market opened higher following positive global cues around the world, Soon after the open the buying in markets has been exhausted as buyers lacked confidence at higher levels due to lack of positive triggers amid rising concerns over COVID-19 inspite of stimulus announced by the governments across the world.
When there's a lot of uncertainty and the buyers lack confidence in taking the markets higher, even the smallest pullbacks turn into bigger falls due to the uncertainty present in the markets. This is one of the main reason the market fell so sharply from highs today.