Leader of supporters supporting supporters in part of orchestra (5)
I believe the answer is:
brass
'part of orchestra' is the definition.
(I've seen this before)
'leader of supporters supporting supporters' is the wordplay.
'leader of' indicates taking the first letters.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'supporters' becomes 'bras' (a bra gives support to breasts).
The initial letter of 'supporters' is 's'.
's' put after 'bras' is 'BRASS'.
'in' is the link.
(Other definitions for brass that I've seen before include "Baggage" , "Gall" , "Instruments, alloy" , "section of orchestra" , "An alloy; part of orchestra" .)