Is critical of the cuffs (6)
I believe the answer is:
knocks
'cuffs' is the definition.
The definition and answer can be both to do with contact as well as being verbs in their -s form.
Perhaps you can see a link between them that I don't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for knocks that I've seen before include "Bangs on door" , "Raps on the door" , "Raps; criticises" , "Hits" , "Raps, taps" .)