Scholar's written about spy in battle (7)
I believe the answer is:
magenta
'battle' is the definition.
(I know that Magenta is a pitched battle)
'scholar's written about spy' is the wordplay.
'scholar' becomes 'ma' (Master of Arts).
'written about' is an insertion indicator.
'spy' becomes 'agent' (secret agent).
'ma' enclosing 'agent' is 'MAGENTA'.
'in' acts as a link.
(Other definitions for magenta that I've seen before include "Bright purplish red or magnate" , "puce" , "this might be an ink" , "A crimson dye" , "Shade of purple" .)