King, but not crowned, protected by staff (6)
I believe the answer is:
canute
'king' is the definition.
(King Canute, 11th-century king)
'but not crowned protected by staff' is the wordplay.
'not crowned' means to remove the first letter (crown could mean the top of the word).
'protected by' is an insertion indicator.
'staff' becomes 'cane' (I've seen this in another clue).
'but' with its first letter taken away is 'ut'.
'ut' put into 'cane' is 'CANUTE'.
(Other definitions for canute that I've seen before include "Old English king who tried to turn the tide" , "English king who commanded tide to go back" , "Danish king of England who tried to stop the tide" , "English king who tried to command the waves" , "The king who thought he could stop the tide" .)