Musical organ behind orchestra leader (6)
I believe the answer is:
oliver
'musical' is the definition.
(I've seen this before)
'organ behind orchestra leader' is the wordplay.
'organ' becomes 'liver' (liver is a kind of organ).
'behind' says to put letters next to each other.
'leader' suggests taking the first letters.
The first letter of 'orchestra' is 'o'.
'liver' after 'o' is 'OLIVER'.
(Other definitions for oliver that I've seen before include "Master Twist" , "Paladin (with Roland)" , "The boy who wanted more" , "Musical (with a Twist!)" , "Lionel Bart musical" .)