Part of shirt collar, perhaps (4)
I believe the answer is:
cuff
I believe this is a double definition.
'part of shirt' is the first definition.
(part of a shirt sleeve)
'collar perhaps' is the second definition.
(both can mean to hit)
(Other definitions for cuff that I've seen before include "A slap" , "Part of a shirt sleeve - hit" , "Blow; end of sleeve" , "[SLEUTH]" , "Sleeve ending" .)