Attack a fool and suffer afterwards (6)
I believe the answer is:
assail
'attack' is the definition.
(I know that attack can be written as assail)
'a fool and suffer afterwards' is the wordplay.
'a fool' becomes 'ass' (both can mean a stupid person).
'and' means one lot of letters go next to another.
'suffer afterwards' becomes 'ail' (ailing is a kind of suffering. I am not sure about the 'afterwards' bit.).
'ass'+'ail'='ASSAIL'
Can you help me to learn more?
(Other definitions for assail that I've seen before include "Attack violently and persistently" , "Assault, attack" , "Set upon" , "Slate" , "Launch an attack" .)