Standard European national supporter (8)
I believe the answer is:
flagpole
'national supporter' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'standard european' is the wordplay.
'standard' becomes 'flag' (standard is a type of flag).
'european' becomes 'pole' (someone from Poland).
'flag'+'pole'='FLAGPOLE'
Can you help me to learn more?
(Other definitions for flagpole that I've seen before include "Standard post" , "standard-bearer" , "means to raise standard" , "Ceremonial mast" , "Pin" .)