Fighter spoiling a dog trial (9)
I believe the answer is:
gladiator
'fighter' is the definition.
(I know that gladiator is a type of fighter)
'spoiling a dog trial' is the wordplay.
'spoiling' is an anagram indicator.
'a'+'dog'+'trial'='adogtrial'
'adogtrial' with letters rearranged gives 'GLADIATOR'.
(Other definitions for gladiator that I've seen before include "Roman arena combatant" , "One trained to fight in Roman arenas" , "one entering the ring" , "Film" , "Gold tiara (anag.)" .)