Drink is the reason for taking chance going topless (6)
I believe the answer is:
'drink' is the definition.
(whisky is a kind of drink)
'the reason for taking chance going topless' is the wordplay.
'the reason for' becomes 'why' (why something happened).
'taking' is an insertion indicator.
'chance' becomes 'risk' (synonyms).
'going topless' means to remove the first letter.
'risk' with its first letter taken off is 'isk'.
'why' placed around 'isk' is 'WHISKY'.
'is' acts as a link.
(Other definitions for whisky that I've seen before include "Grain alcohol" , "Alcoholic drink" , "Scotch" , "W in radio alphabet" , "Spirit distilled from malted grain" .)