Smoothly or impartially (6)
I believe the answer is:
evenly
This clue is a double definition.
'smoothly' is the first definition.
(I've seen this before)
'impartially' is the second definition.
(thesaurus)
(Other definitions for evenly that I've seen before include "In a level and regular way" , "Smoothly or fairly" , "In a balanced or impartial way" , "Calmly or equitably" , "not getting ruffled" .)