Leader of the best section of the orchestra (3,5)
I believe the answer is:
top brass
'leader of' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'best section of the orchestra' is the wordplay.
'best' becomes 'top' (top can mean the very best).
'section of the orchestra' becomes 'brass' (brass section in an orchestra).
'top'+'brass'='TOP-BRASS'
'the' is the link.
Can you help me to learn more?
(Other definitions for top brass that I've seen before include "People in authority (informal)" , "VIPs" , "Highest-ranking officials with best yellow alloy" , "Senior military personnel" , "The people in charge (of the Army?)" .)