Raising support at small grounds (6)
I believe the answer is:
stadia
'grounds' is the definition.
(I've seen this before)
'raising support at small' is the wordplay.
'raising' is a reversal indicator (in a down clue, letters go up).
'support' becomes 'aid' (to aid is to help or support).
'small' becomes 's' (abbreviation - e.g. clothes size).
'aid'+'at'+'s'='aidats'
'aidats' back-to-front is 'STADIA'.
(Other definitions for stadia that I've seen before include "Bowls" , "Sports arenas" , "large arenas" , "Sports grounds" , "Athletics grounds" .)