Strip support over head getting promoted (6)
I believe the answer is:
ribbon
'strip' is the definition.
(I know that ribbon is a type of strip)
'support over head getting promoted' is the wordplay.
'support' becomes 'rib' (type of architectural support).
'over' says to put letters next to each other.
'head' becomes 'nob' (I've seen this in other clues).
'getting promoted' says the letters should be written in reverse (in a down clue, letters go up).
'nob' reversed gives 'bon'.
'rib'+'bon'='RIBBON'
(Other definitions for ribbon that I've seen before include "Narrow strip of coloured cloth, worn as ornament" , "Thin strip of cloth" , "Streamer" , "Strip of ornamental cloth as for hair" , "Narrow strip of fabric" .)