Coarse Yankee supporting Republican in win (6)
I believe the answer is:
grainy
'coarse' is the definition.
(I've seen this before)
'yankee supporting republican in win' is the wordplay.
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'republican' becomes 'r' (abbreviation).
'in' indicates putting letters inside.
'win' becomes 'gain' ('gain' can be a synonym of 'win'**).
'r' going inside 'gain' is 'grain'.
'y' put after 'grain' is 'GRAINY'.
(Other definitions for grainy that I've seen before include "Old still can be this" , "Granular" , "(Of photo) having low resolution" , "gravelly" , "not clear" .)