Rogue rats out deputy (9)
I believe the answer is:
surrogate
'deputy' is the definition.
(I know that Surrogate is a type of deputy)
'rogue rats out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'rogue'+'rats'='roguerats'
'roguerats' with letters rearranged gives 'SURROGATE'.
(Other definitions for surrogate that I've seen before include "stand-in" , "Argues about rot with substitute or deputy" , "Substitute fulfilling the role of another" , "One standing in" , "Deputising substitute" .)