Start off, humiliate headquarters (4)
I believe the answer is:
base
'headquarters' is the definition.
(I've seen this before)
'start off humiliate' is the wordplay.
'start off' means to remove the first letter (I've seen 'starting off' mean this (the starting letter is removed)).
'humiliate' becomes 'abase' (synonyms).
'abase' with its initial letter removed is 'BASE'.
(Other definitions for base that I've seen before include "Reprobate" , "Interest charged by the Bank of England to commercial banks" , "Ignoble - foundation" , "Found - worthless" , "Foot; ignoble" .)