Execute extremely brave leader (6)
I believe the answer is:
behead
'execute' is the definition.
(I know that behead is a more specific form of the action execute)
'extremely brave leader' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'leader' becomes 'head' (head is a kind of leader).
'brave' with its centre removed is 'be'.
'be'+'head'='BEHEAD'
(Other definitions for behead that I've seen before include "Carry out execution" , "Guillotine" , "Remove cranium as in old execution" , "Knock someone's block off?" , "Remove the crown" .)