A chap in rep (5)
I believe the answer is:
agent
'rep' is the definition.
(I've seen this before)
'a chap' is the wordplay.
'chap' becomes 'gent' (I've seen this in other clues**).
'a'+'gent'='AGENT'
'in' is the link.
(Other definitions for agent that I've seen before include "Spy - broker" , "Substance that exerts some force or effect" , "Actors' manager" , "Operative" , "factor in Scotland" .)