Trouble dogs American behind attack (6)
I believe the answer is:
assail
'attack' is the definition.
(I know that assail can be written as assail)
'trouble dogs american behind' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'dogs' says to put letters next to each other (dogs can mean follows or chases).
'american behind' becomes 'ass' (primarily US term for one's behind).
'ail' after 'ass' is 'ASSAIL'.
(Other definitions for assail that I've seen before include "storm" , "Beset" , "Launch an attack" , "Molest or harass" , "Criticise severely" .)