Spirit shown by rebel fighters (3)
I believe the answer is:
elf
'spirit' is the definition.
(magical creature)
'shown by rebel fighters' is the wordplay.
'shown by' says the answer is hidden in the clue.
'ELF' is hidden in the letters of 'rebel fighters'.
(Other definitions for elf that I've seen before include "Goblin" , "He causes mischief" , "Mischievous sprite" , "Small creature" , "Imp-like being" .)