Snubs fans supporting Forest essentially (7)
I believe the answer is:
rebuffs
'snubs' is the definition.
('rebuff' can be a synonym of 'snub')
'fans supporting forest essentially' is the wordplay.
'fans' becomes 'buffs' ('buff' can be a synonym of 'fan').
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'essentially' indicates the central letters.
The centre of 'forest' is 're'.
'buffs' after 're' is 'REBUFFS'.
(Other definitions for rebuffs that I've seen before include "Rejects outright and bluntly" , "Brushes off" , "Checks" , "Rejects abruptly" , "Snubs" .)