Defender with axe and boomerang (8)
I believe the answer is:
backfire
'boomerang' is the definition.
(synonyms)
'defender with axe' is the wordplay.
'defender' becomes 'back' (I've seen this before).
'with' means one lot of letters go next to another.
'axe' becomes 'fire' (both can mean to dismiss or sack).
'back'+'fire'='BACKFIRE'
'and' acts as a link.
(Other definitions for backfire that I've seen before include "Rebound on oneself" , "Go wrong" , "report" , "Have an unintended negative consequence" , "Have the opposite and damaging effect to that intended" .)