Constrains troops
I believe the answer is:
forces
This clue could be a double definition.
'constrains' is the first definition.
The answer and definition can be both to do with contact as well as being verbs in their -s form.
Maybe there's a link between them I don't understand?
'troops' is the second definition.
(I've seen this in another clue)
Can you help me to learn more?
(Other definitions for forces that I've seen before include "Troops and weaponry" , "Compels or inflicts" , "Military and police, say" , "Troops; makes" , "Compel's the military" .)