Young copper's arresting bishop (4)
I believe the answer is:
cubs
'young' is the definition.
'copper's arresting bishop' is the wordplay.
'copper's' becomes 'Cu's' (Cu is the chemical symbol for copper).
'arresting' is an insertion indicator.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'cus' going around 'b' is 'CUBS'.
(Other definitions for cubs that I've seen before include "Little foxes" , "Young wolves" , "Young and inexperienced reporters" , "Whelps" , "Young bears" .)