Fighting security measure, he may leave you spellbound (7)
I believe the answer is:
warlock
'he may leave you spellbound' is the definition.
(warlocks cast spells)
'fighting security measure' is the wordplay.
'fighting' becomes 'war' ().
'security measure' becomes 'lock'.
'war'+'lock'='WARLOCK'
(Other definitions for warlock that I've seen before include "Sorcerer" , "Magician; Peter ---, composer" , "Necromancer" , "Male magician - British composer, 1894-1930 - low rack (anag)" , "Charmer" .)