Hector's boast about partner (8)
I believe the answer is:
ballyrag
'hector's' is the definition.
(synonyms)
'boast about partner' is the wordplay.
'boast' becomes 'brag' (brag is a kind of boast).
'about' means one lot of letters goes inside another.
'partner' becomes 'ally' (an ally is an associate or supporter).
'brag' going around 'ally' is 'BALLYRAG'.
(Other definitions for ballyrag that I've seen before include "Browbeat, boss around" , "Intimidate" , "Browbeat, hector" .)