Supporter very obviously just started cheer (5)
I believe the answer is:
bravo
'cheer' is the definition.
(bravo is a kind of cheer)
'supporter very obviously just started' is the wordplay.
'supporter' becomes 'bra' (I've seen this before).
'just started' says to take the initial letters (I've seen 'just starting' mean this).
The initial letters of 'very obviously' is 'vo'.
'bra'+'vo'='BRAVO'
(Other definitions for bravo that I've seen before include "Exclamation of approval" , "next to alpha" , "Theatrical 'well done'" , "Thug, hired assassin; B (in radio communication)" , "B in radio communications" .)