Shoot ringleader in gang, troublemaker (9)
I believe the answer is:
firebrand
'troublemaker' is the definition.
(thesaurus)
'shoot ringleader in gang' is the wordplay.
'shoot' becomes 'fire' (firing is a kind of shooting**).
'ringleader' becomes 'r' (first letter of ring).
'in' means one lot of letters goes inside another.
'gang' becomes 'band' (I've seen this before).
'r' put within 'band' is 'brand'.
'fire'+'brand'='FIREBRAND'
(Other definitions for firebrand that I've seen before include "Troublemaker" , "Energetic person often fomenting trouble" , "Rabble-rouser" , "One who stirs up trouble" , "Agitator" .)