Bullfighter in Benidorm, at a do, relaxing (7)
I believe the answer is:
matador
'bullfighter' is the definition.
('matador' can be a synonym of 'bullfighter')
'in benidorm at a do relaxing' is the wordplay.
'in' says the answer is hidden in the clue.
'MATADOR' is hidden within 'benidorm at a do relaxing'.
(Other definitions for matador that I've seen before include "Beastly fighting man" , "A Spanish bullfighter" , "fighter in the ring?" , "Ring butcher" , "Spanish killer" .)