Knock family for being rustic (7)
I believe the answer is:
bumpkin
'being rustic' is the definition.
(I've seen this before)
'knock family' is the wordplay.
'knock' becomes 'bump' (synonyms).
'family' becomes 'kin' (synonyms).
'bump'+'kin'='BUMPKIN'
'for' acts as a link.
(Other definitions for bumpkin that I've seen before include "Daft countryman" , "Clumsy rustic" , "Country cousin" , "Country person with awkward manners" , "Peasant" .)