Scottish dance about to be supported by the Spanish (4)
I believe the answer is:
reel
'scottish dance' is the definition.
(I've seen this before)
'about to be supported by the spanish' is the wordplay.
'about' becomes 're' (regarding).
'to be supported by' means one lot of letters go next to another (letters go below - in down clue).
'the spanish' becomes 'el'.
're'+'el'='REEL'
(Other definitions for reel that I've seen before include "Stagger in Irish dance" , "Lively Scottish dance" , "Rock" , "Film spool" , "Dance - sway - cotton holder" .)