Begin to organise a drinking bout (5)
I believe the answer is:
binge
'a drinking bout' is the definition.
(I've seen this before)
'begin to organise' is the wordplay.
'to organise' indicates anagramming the letters (I've seen 'organising' mean this).
'begin' anagrammed gives 'BINGE'.
(Other definitions for binge that I've seen before include "A drinking bout" , "Eat greedily" , "Period of overindulgence" , "Bout of indulgence" , "Period of excess" .)