North American imperfections backing spurious argument (5,3)
I believe the answer is:
straw man
'spurious argument' is the definition.
(I've seen this before)
'north american imperfections backing' is the wordplay.
'north' becomes 'N' (synonyms).
'american' becomes 'Am' (abbreviation in some contexts).
'imperfections' becomes 'warts' (I can't justify this - if you can you should believe this answer much more).
'backing' says the letters should be written backwards.
'n'+'am'+'warts'='namwarts'
'namwarts' in reverse letter order is 'STRAW MAN'.
Can you help me to learn more?
(Other definitions for straw man that I've seen before include "Ineffective figurehead" , "Person of no substance" , "Argument put forward to stimulate discussion" , "Wants arm about kind of fallacy - or scarecrow" , "fake" .)