Nothing held one back in this state (5)
I believe the answer is:
idaho
'in this state' is the definition.
(I've seen this before)
'nothing held one back' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'held' becomes 'had' ('have' can be a synonym of 'hold').
'one' becomes 'i' (Roman numeral).
'back' says the letters should be written backwards.
'o'+'had'+'i'='ohadi'
'ohadi' written backwards gives 'IDAHO'.
(Other definitions for idaho that I've seen before include "part of US near Washington" , "US location" , "North-western state of America" , "Pertaining to the Bard" , "US state, capital Boise" .)