Wise man going through American customs? (6)
I believe the answer is:
usages
'customs?' is the definition.
('usage' can be a synonym of 'custom')
'wise man going through american' is the wordplay.
'wise man' becomes 'sage' (sage is a kind of wise man).
'going through' is an insertion indicator.
'american' becomes 'US' (United States).
'sage' going inside 'us' is 'USAGES'.
(Other definitions for usages that I've seen before include "speech patterns" , "Linguistic norms" , "Habitual or customary practices" , "Customary treatments, practices" , "Customs." .)