Informed A&E about fighting (5)
I believe the answer is:
aware
'informed' is the definition.
(I've seen this before)
'ae about fighting' is the wordplay.
'about' means one lot of letters goes inside another.
'fighting' becomes 'war'.
'ae' placed around 'war' is 'AWARE'.
(Other definitions for aware that I've seen before include "Conscious or having knowledge of" , "Conscious, knowing about" , "well informed" , "Knowing (of something)" , "Acquainted with or mindful of" .)