Island's secret society backing racket within (8)
I believe the answer is:
trinidad
'island's' is the definition.
(Trinidad is an example)
'secret society backing racket within' is the wordplay.
'secret society' becomes 'triad' (I've seen this before).
'backing' shows that the letters should be reversed in order.
'racket' becomes 'din' (I've seen this before).
'within' is an insertion indicator.
'din' written backwards gives 'nid'.
'triad' going around 'nid' is 'TRINIDAD'.
(Other definitions for trinidad that I've seen before include "English-speaking island off Venezuela" , "... [WI ISLAND]" , "W. I. island" , "Island linked to Tobago" , "Port of Spain island" .)