English playmaker Jack heading for nightclub in drag (7)
I believe the answer is:
osborne
'english playmaker' is the definition.
(playwright John Osborne)
'jack heading for nightclub in drag' is the wordplay.
'jack' becomes 'OS' (Ordinary Seaman - jack can mean a sailor).
'heading for' indicates taking the first letters.
'in' is an insertion indicator.
'drag' becomes 'bore' (drag can mean something boring).
The first letter of 'nightclub' is 'n'.
'n' placed within 'bore' is 'borne'.
'os'+'borne'='OSBORNE'
(Other definitions for osborne that I've seen before include "Queen Victoria's IOW house" , "Chancellor" , "John --, English dramatist" , "Q. Victoria's IOW home" , "grand island house" .)