Fend off leader of pirates in film (5)
I believe the answer is:
repel
'fend off' is the definition.
(I've seen this before)
'leader of pirates in film' is the wordplay.
'leader of' suggests taking the first letters.
'in' is an insertion indicator.
'film' becomes 'reel' (reel is a kind of film).
The first letter of 'pirates' is 'p'.
'p' put within 'reel' is 'REPEL'.
(Other definitions for repel that I've seen before include "Drive back like leper" , "give you the creeps" , "Drive back, rebuff" , "Nauseate" , "Sicken" .)