One maybe hammered in the main, back in scrapes (7)
I believe the answer is:
abrades
'scrapes' is the definition.
('abrade' can be a synonym of 'scrape')
'one maybe hammered in the main back' is the wordplay.
'one maybe hammered' becomes 'brad' (brad is a type of nail).
'in the' is an insertion indicator.
'main' becomes 'sea' (the main is an old name for the sea).
'back' says the letters should be written backwards.
'sea' in reverse letter order is 'aes'.
'brad' going within 'aes' is 'ABRADES'.
'in' acts as a link.
(Another definition for abrades that I've seen is " Scratches".)