Says fresh trial is a little less impartial (7)
I believe the answer is:
neutral
'impartial' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for neutral that I've seen before include "Gear position" , "nondescript colour" , "Indifferent; not in gear" , "Inoffensive; beige colour" , "Disengaged transmission situation" .)