Rough game is supported by lowest social classes (4)
I believe the answer is:
rude
'rough' is the definition.
('rude' can be similar in meaning to 'rough')
'game is supported by lowest social classes' is the wordplay.
'game' becomes 'ru' (rugby union).
'is supported by' is a charade indicator (letters next to each other) (letters go below - in down clue).
'lowest social classes' becomes 'de' (social class grades used in demographics).
'ru'+'de'='RUDE'
(Other definitions for rude that I've seen before include "discourtesy" , "Coarse or discourteous" , "Impolite or vulgar" , "lacking refinement" , "Ill-mannered; hearty" .)