Drunk losing head in game of chance (5)
I believe the answer is:
lotto
'game of chance' is the definition.
(I've seen this before)
'drunk losing head' is the wordplay.
'drunk' becomes 'blotto' (I've seen this before).
'losing head' means to remove the first letter.
'blotto' with its first letter taken off is 'LOTTO'.
'in' is the link.
(Other definitions for lotto that I've seen before include "form of gambling" , "Bingo-like game" , "chancy business" , "Children's game, housey-housey" , "Game of chance based on numbered balls being drawn at random" .)