Equipment army used to imprison resistance (3,4)
I believe the answer is:
leg iron
'equipment' is the definition.
I know nothing about this answer so I can't tell whether this works.
'army used to imprison resistance' is the wordplay.
I cannot really see how this works, but
'resistance' could be 'r' (electronics abbreviation) and 'r' is located in the answer.
'army' could be 'legion' (legion is a kind of army) and 'legion' is present in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for leg iron that I've seen before include "Fetter" , "which delays flight indefinitely" , "Ankle restraint for a prisoner" , "restriction put on pin" .)