Fight decrease in stuff for recycling (5,4)
I believe the answer is:
scrap iron
'stuff for recycling' is the definition.
'fight decrease' is the wordplay.
'fight' becomes 'scrap' (I've seen this before).
'decrease' becomes 'iron' (de-crease: remove creases by ironing).
'scrap'+'iron'='SCRAP-IRON'
'in' is the link.
(Other definitions for scrap iron that I've seen before include "Waste metal for melting down" , "Discarded metal" , "rubbish" , "for recycling" .)