Triumph, confining prisoners on island state (9)
I believe the answer is:
wisconsin
'state' is the definition.
(Wisconsin is an example)
'triumph confining prisoners on island' is the wordplay.
'triumph' becomes 'win' (I've seen this before).
'confining' means one lot of letters goes inside another.
'prisoners' becomes 'cons'.
'on' is a charade indicator (letters next to each other).
'island' becomes 'is'.
'cons' put after 'is' is 'iscons'.
'win' placed around 'iscons' is 'WISCONSIN'.
(Other definitions for wisconsin that I've seen before include "US state bordering Lakes Superior and Michigan" , "The "Badger State"" , "State of N. central US" , "US state, capital Madison" , "Northern state" .)