Troops failing to engage? (10)
I believe the answer is:
detachment
'troops' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for detachment that I've seen before include "Objective state; group of troops" , "Military unit" , "some engaged in military action?" , "Aloofness" , "indifference" .)