Shackle hard with copper very loudly (8)
I believe the answer is:
handcuff
'shackle' is the definition.
(handcuffing is a kind of shackling)
'hard with copper very loudly' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'with' becomes 'and'.
'copper' becomes 'cu' (chemical symbol).
'very loudly' becomes 'ff'.
'h'+'and'+'cu'+'ff'='HANDCUFF'
(Other definitions for handcuff that I've seen before include "Restrain (one arrested)" , "Shackle by the wrist" , "Manacle" , "Put bracelets on" , "Restrict movement" .)