Trouble following fool's attack (6)
I believe the answer is:
assail
'attack' is the definition.
(synonyms)
'trouble following fool's' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'following' means one lot of letters go next to another.
'fool's' becomes 'ass' (ass is a kind of fool).
'ail' put after 'ass' is 'ASSAIL'.
(Other definitions for assail that I've seen before include "Aggressively attack" , "Assault, attack" , "Slate" , "Beset" , "storm" .)