Boxer's restraint (5)
I believe the answer is:
leash
'boxer's restraint' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leash that I've seen before include "Bind" , "Restraining strap for dog" , "Line for controlling a dog" , "(Dog's) lead" , "Rope to control dog" .)