Brief flash in battle (4)
I believe the answer is:
spar
'battle' is the definition.
(thesaurus)
'brief flash' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'flash' becomes 'spark' (spark is a kind of flash).
'spark' with its last letter removed is 'SPAR'.
'in' acts as a link.
(Other definitions for spar that I've seen before include "Act as boxer" , "Shadow-box" , "Mineral; strong pole" , "Box - mineral - rod" , "piece of wood?" .)