Fight in this party (4)
I believe the answer is:
spar
'fight' is the definition.
(I know that spar is a more specific form of fight)
'in this party' is the wordplay.
'in' says the answer is hidden in the clue.
'SPAR' can be found hidden inside 'this party'.
(Other definitions for spar that I've seen before include "Engage in argument" , "Translucent mineral" , "Box in training - mineral" , "Box; mineral; pole" , "A mineral; nautical pole" .)