Fool suffered when attacked (8)
I believe the answer is:
assailed
'attacked' is the definition.
('assail' can be a synonym of 'attack')
'fool suffered' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'suffered' becomes 'ailed' (ailing is a kind of suffering).
'ass'+'ailed'='ASSAILED'
'when' acts as a link.
(Other definitions for assailed that I've seen before include "Attacked, lashed out" , "charged" , "Went for" , "Set upon" , "Under attack" .)