Genuine support for a team of stars (8)
I believe the answer is:
sidereal
'of stars' is the definition.
(sidereal means relating to the stars)
'genuine support for a team' is the wordplay.
'genuine' becomes 'real' (associated in meaning).
'support for' means one lot of letters go next to another.
'a team' becomes 'side' (both can mean a sports team).
'real' put after 'side' is 'SIDEREAL'.
(Other definitions for sidereal that I've seen before include "Of the stars or constellations" , "Of or measured by the stars" , "Relating to the constellations" , "involving stars" , "Relating to the distant stars" .)