Metal debris left in battle (5)
I believe the answer is:
scrap
'battle' is the definition.
(I know that scrap is a type of battle)
'metal debris left in' is the wordplay.
'metal' becomes 'Cr' (Cr is an example).
'debris left' becomes 'sap' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'cr' inserted into 'sap' is 'SCRAP'.
Can you help me to learn more?
(Other definitions for scrap that I've seen before include "Tussle over junk metal?" , "Tiny piece; abolish" , "Abolish; leftover" , "Fragment or morsel" , "row" .)