Demands fool accepts king (4)
I believe the answer is:
asks
'demands' is the definition.
(I know this)
'fool accepts king' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'accepts' is an insertion indicator.
'king' becomes 'K' (abbreviation for king in chess).
'ass' placed around 'k' is 'ASKS'.
(Other definitions for asks that I've seen before include "Puts a question" , "Puts a query" , "Begs" , "Poses a question" , "Requests information about" .)