Cobblers pursue proctor's assistant (7)
I believe the answer is:
bulldog
'proctor's assistant' is the definition.
(assistants to a proctor were called bulldogs)
'cobblers pursue' is the wordplay.
'cobblers' becomes 'bull' (slang for a man's testicles).
'pursue' becomes 'dog' (dogging is a kind of pursuing).
'bull'+'dog'='BULLDOG'
(Other definitions for bulldog that I've seen before include "Sort of clip" , "Breed of canine; stationery clip" , "Animal symbolising the British" , "attached to lead" , "Tenacious type" .)