A judge comes down on US guitar hero (classical) (4)
I believe the answer is:
ajax
'us guitar hero classical' is the definition.
I can't judge whether this defines the answer.
'a judge comes down' is the wordplay.
'judge' becomes 'J' (abbreviation for judge).
'comes down' becomes 'ax' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'j'+'ax'='AJAX'
'on' acts as a link.
Can you help me to learn more?
(Other definitions for ajax that I've seen before include "Ancient Greek hero" , "classic war hero" , "Cleaner" , "Hero of Greek mythology" , "old privy" .)