Band around the neck (6)
I believe the answer is:
'band around the neck' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for collar that I've seen before include "Apprehend (someone)" , "Item worn around the neck" , "Seize; cut of bacon" , "Neckband to seize" , "Apprehend (colloq.); cut of bacon" .)