He is in court with a strong case (5)
I believe the answer is:
chest
'case' is the definition.
(both are types of container)
'he is in court with a strong' is the wordplay.
'is in' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'with' means one lot of letters goes inside another.
'a strong' becomes 's' (this could be a standard abbreviation I've not previously seen).
'ct' enclosing 's' is 'cst'.
'he' put into 'cst' is 'CHEST'.
Can you help me to learn more?
(Other definitions for chest that I've seen before include "ark" , "Strong box; thorax" , "Treasure box?" , "Strongbox; sternum" , "Box or trunk" .)