Collared (8)
I believe the answer is:
arrested
'collared' is the definition.
('arrest' can be a synonym of 'collar')
This is all the clue.
(Other definitions for arrested that I've seen before include "Taken into custody or stopped" , "captured" , "Taken into police custody" , "Taken into custody, being serrated" , "Seized and took into custody" .)