Blockhead is not well from attacks (7)
I believe the answer is:
assails
'attacks' is the definition.
('assail' can be a synonym of 'attack')
'blockhead is not well' is the wordplay.
'blockhead' becomes 'ass' (I've seen this in another clue).
'is not well' becomes 'ails' (I've seen this in another clue).
'ass'+'ails'='ASSAILS'
'from' is the link.
(Other definitions for assails that I've seen before include "storms" , "Attacks" .)