Trouble after silly attack (6)
I believe the answer is:
assail
'attack' is the definition.
(I know that attack can be written as assail)
'trouble after silly' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'after' says to put letters next to each other.
'silly' becomes 'ass'.
'ail' after 'ass' is 'ASSAIL'.
(Other definitions for assail that I've seen before include "Go for" , "storm" , "Sudden attack" , "Criticize" , "Criticise severely" .)