Big cheese? Awful, beginning to crumble and flipping go off (8)
I believe the answer is:
director
'big cheese?' is the definition.
'awful beginning to crumble and flipping go off' is the wordplay.
'awful' becomes 'dire' ('dire' can be a synonym of 'awful'**).
'beginning to' indicates taking the first letters.
'and' is a charade indicator (letters next to each other).
'flipping' shows that the letters should be reversed in order.
'go off' becomes 'rot' (I've seen this before).
The initial letter of 'crumble' is 'c'.
'rot' reversed gives 'tor'.
'dire'+'c'+'tor'='DIRECTOR'
(Other definitions for director that I've seen before include "Company board member" , "One on board" , "This person could be on board or in theatre" , "leader" , "Senior person in a firm, executive or non-executive" .)