Quick raid capturing the pierhead (5)
I believe the answer is:
rapid
'quick' is the definition.
('rapid' can be a synonym of 'quick')
'raid capturing the pierhead' is the wordplay.
'capturing' indicates putting letters inside.
'the pierhead' becomes 'p' (head letter of 'pier').
'raid' enclosing 'p' is 'RAPID'.
(Other definitions for rapid that I've seen before include "Fast, quick" , "Swift, speedy" , "Showing pace" , "Precipitate" , "Happening quickly" .)