Troops behaving impartially (10)
I believe the answer is:
detachment
'troops' 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 detachment that I've seen before include "inclination to keep to the objective" , "reserve" , "squad" , "Objective state; group of troops" , "Unit of soldiers" .)