Dodgy American quietly infiltrating group (7)
I believe the answer is:
suspect
'dodgy' is the definition.
(I've seen this before)
'american quietly infiltrating group' is the wordplay.
'american' becomes 'us'.
'quietly' becomes 'p' (p for piano and quiet).
'infiltrating' indicates putting letters inside.
'group' becomes 'sect' (I've seen this in other clues**).
'us'+'p'='usp'
'usp' placed within 'sect' is 'SUSPECT'.
(Other definitions for suspect that I've seen before include "Presume" , "One is believed to be guilty but without proof" , "Have reason to believe" , "Funny" , "Be ready to believe - one of the usual crowd?" .)