Fool was unwell, being attacked (8)
I believe the answer is:
assailed
'being attacked' is the definition.
(I've seen this before)
'fool was unwell' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'was unwell' becomes 'ailed' (I've seen this in another clue).
'ass'+'ailed'='ASSAILED'
(Other definitions for assailed that I've seen before include "Set upon" , "became aggressive" , "Under attack" , "Attacked, lashed out" , "charged" .)