Enthusiast heard you are supporting America over China (7)
I believe the answer is:
amateur
'enthusiast' is the definition.
(I've seen this before)
'you are supporting america over china' is the wordplay.
'you are' becomes 'ur' (text or internet abbreviation).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'china' becomes 'mate' (china plate is Cockney rhyming slang for mate).
'a'+'mate'='amate'
'ur' after 'amate' is 'AMATEUR'.
'heard' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for amateur that I've seen before include "11 [UNTRAINED]" , "lacking professionalism" , "Lay person" , "lacking professional expertise" , "Of sportsman, not professional" .)