Island beginning to show passion supporting volunteers (8)
I believe the answer is:
tasmania
'island' is the definition.
(Tasmania is an example)
'beginning to show passion supporting volunteers' is the wordplay.
'beginning to' says to take the initial letters.
'passion' becomes 'mania' ('mania' can be a synonym of 'passion'**).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
The first letter of 'show' is 's'.
's'+'mania'='smania'
'smania' after 'ta' is 'TASMANIA'.
(Other definitions for tasmania that I've seen before include "Australian island to south of Bass Strait" , "Pacific island" , "Van Diemen's Land" , "somewhere in Antipodes?" , "State off 23 [VICTORIA]" .)