European supporter up for song (4)
I believe the answer is:
tune
'song' is the definition.
(I've seen this in another clue)
'european supporter up' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'supporter' becomes 'nut' (I can't explain this - if you can you should believe this answer much more).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'e'+'nut'='enut'
'enut' written backwards gives 'TUNE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for tune that I've seen before include "Air, melody" , "strain" , "Adjust a radio receiver to a frequency" , "Of engine, adjust to run smoothly" , "Optimise the condition of" .)