Queen's supporting band (heavy metal) and will be instigator (10)
I believe the answer is:
ringleader
'instigator' is the definition.
(ringleader is a kind of instigator)
'queen's supporting band heavy metal' is the wordplay.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'band' becomes 'ring' (ring is a kind of band).
'heavy metal' becomes 'lead' (lead is a heavy metal).
'ring'+'lead'='ringlead'
'er' after 'ringlead' is 'RINGLEADER'.
'and will be' is the link.
(Other definitions for ringleader that I've seen before include "Chief mischief-maker" , "One heading up illicit activity" , "firebrand" , "Chief troublemaker" , "Chief mischief maker" .)