Self-confidence of orchestra section (5)
I believe the answer is:
brass
I believe this clue is a double definition.
'self-confidence' is the first definition.
(brass can mean courage or confidence)
'orchestra section' is the second definition.
(brass section in an orchestra)
'of' is the link.
(Other definitions for brass that I've seen before include "Impertinence" , "Yellowish alloy" , "Alloy; money" , "Alloy of copper and zinc" , "Ready" .)