Portray agent with grudge (9)
I believe the answer is:
represent
'portray' is the definition.
(I know this)
'agent with grudge' is the wordplay.
'agent' becomes 'rep' (short for representative).
'with' says to put letters next to each other.
'grudge' becomes 'resent' (I've seen this before).
'rep'+'resent'='REPRESENT'
(Other definitions for represent that I've seen before include "Stand for or symbolise" , "Mean" , "Speak on behalf" , "Picture" , "declare" .)