What is Bearish Butterfly?
A Bearish Butterfly is a harmonic pattern which provides more accuracy comparative to classical shapes.
The butterfly is a reversal pattern that allows you to trade at extreme points in terms of high and lows.
The criteria for a Bearish Butterfly is that the prevailing trend of the stock price should be bullish and the extreme point must be confirmed with some other price pattern, like wedge shapes.
Here in ICICI BANK its a Rising Wedge shape in long term which is resembling with a Bearish Butterfly formation on the top.
Also Fibonacci retracement levels must confirm the price pattern.
So selling is being initiated at around 320-325 levels for the minimum target of 300.
This is only an observation on behalf of technical analysis, please correlate the same before investing.
Here is the snapshot. 
