Participants in fast rallies emanating from stars (6)
I believe the answer is:
astral
'emanating from stars' is the definition.
(I've seen this in another clue)
'participants in fast rallies' is the wordplay.
'participants in' indicates a hidden word.
'ASTRAL' is hidden within 'fast rallies'.
(Other definitions for astral that I've seen before include "Pertaining to the stars" , "Characteristic of stars" , "Like the stars" , "Altars (anag)" , "Starry sort of altars." .)