Smiles unevenly supporting supporter's club (7)
I believe the answer is:
brassie
'club' is the definition.
(I know that brassie is a type of wood)
'smiles unevenly supporting supporter's' is the wordplay.
'unevenly' means one should take alternating letters (letters in odd-numbered positions rather than even).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'supporter's' becomes 'bra's' (a bra gives support to breasts).
The alternating letters of 'smiles' are 'sie'.
'sie' put after 'bras' is 'BRASSIE'.
(Other definitions for brassie that I've seen before include "old wood" , "Golf-club" , "Old golf club" , "Number two wood (golf)" .)