Head off on getting stick (6)
I believe the answer is:
adhere
'stick' is the definition.
(to adhere to something is to stick to it)
'head off on getting' is the wordplay.
'off' is an anagram indicator.
'on' becomes 're' ('on' can be mean 'with reference to').
'getting' says to put letters next to each other.
'head' is an anagram of 'adhe'.
'adhe'+'re'='ADHERE'
(Other definitions for adhere that I've seen before include "Stick to as by suction" , "Stick - join" , "Stick to, remain loyal" , "Hold fast, stand by" , "Stick like a stamp" .)