Do something in American court (3)
I believe the answer is:
act
'do something' is the definition.
(to act is to do something)
'american court' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'court' becomes 'ct' (abbreviation used in road names).
'a'+'ct'='ACT'
'in' is the link.
(Other definitions for act that I've seen before include "Perform - part of a play" , "Behave like thespian" , "Feign" , "Accomplishment" , "Produce an effect" .)