Restrain two females going after copper (4)
I believe the answer is:
cuff
'restrain' is the definition.
(I know that cuff is a more specific form of fetter)
'two females going after copper' is the wordplay.
'two females' becomes 'ff' (an abbreviation for female written twice).
'going after' says to put letters next to each other.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'ff' put after 'cu' is 'CUFF'.
(Other definitions for cuff that I've seen before include "End part of sleeve" , "Blow - it's on shirt!" , "Hit with the flat of the hand" , "by one hand" , "beat" .)