Wore bra uncomfortably in fight (4,3)
I believe the answer is:
boer war
'fight' is the definition.
'wore bra uncomfortably' is the wordplay.
'uncomfortably' indicates anagramming the letters.
'wore'+'bra'='worebra'
'worebra' with letters rearranged gives 'BOER WAR'.
'in' acts as a link.
(Other definitions for boer war that I've seen before include "1880-81 or 1899-1902 conflict" , "Conflict in southern Africa" , "Fighting" , "Either of two conflicts fought by Britain in S Africa" , "'One of two armed conflicts in southern Africa (4,3)'" .)