Scrap he saw developing into total defeat (9)
I believe the answer is:
whitewash
'total defeat' is the definition.
(thesaurus)
'scrap he saw developing' is the wordplay.
'scrap' becomes 'whit' (both can mean a tiny amount).
'developing' indicates anagramming the letters.
'he'+'saw'='hesaw'
'hesaw' is an anagram of 'ewash'.
'whit'+'ewash'='WHITEWASH'
'into' acts as a link.
(Other definitions for whitewash that I've seen before include "Lime solution; cover up" , "overwhelming defeat" , "Gloss over faults with wall colouring?" , "Deliberate cover-up of faults" , "Cover up - wall coating" .)