Copper's bored by following his usual restraint (5)
I believe the answer is:
cuffs
'restraint' is the definition.
(cuffs is a kind of restraint)
'copper's bored by following' is the wordplay.
'copper's' becomes 'Cu's' (Cu is the chemical symbol for copper).
'bored by' indicates putting letters inside (to bore something can mean to drill into it).
'following' becomes 'ff' (abbreviation used in citations).
'cus' placed around 'ff' is 'CUFFS'.
'his usual' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cuffs that I've seen before include "Ends of sleeves" , "bracelets" , "Open-handed blows" , "Arresting items" , "Rings round to restrain" .)