ACC can be shorted because of a head and shoulder that's formed over a very long period. It can be shorted for a period of 3 months plus. THIS IS A LONG TERM TRADE. Its not meant for a short term period of time. It can be traded over a period of 3 months plus.
You could short it because 21 Weighted Moving Average is hitting the current candlestick and is now giving a bearish move. Its respecting the current downward trend line and you can expect it to fall more. You can keep the stop loss and target as mentioned over here.