Put handcuffs on rarest criminal (6)
I believe the answer is:
arrest
'put handcuffs on' is the definition.
(I've seen this in another clue)
'rarest criminal' is the wordplay.
'criminal' indicates anagramming the letters.
'rarest' anagrammed gives 'ARREST'.
(Other definitions for arrest that I've seen before include "Take into legal custody" , "Detain under suspicion of criminal behaviour" , "Stop, check (progress)" , "Run in" , "Seize (a crime suspect)" .)