Turned out the one inside is new (7)
I believe the answer is:
untried
'new' is the definition.
('untried' can be a synonym of 'new')
'turned out the one inside' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'the one' becomes 'i' (Roman numeral).
'inside' is an insertion indicator.
'turned' anagrammed gives 'untred'.
'untred' placed around 'i' is 'UNTRIED'.
'is' is the link.
(Other definitions for untried that I've seen before include "Intrude, being not yet tested" , "virgin" , "Not given proper hearing in court" , "Intrude (anag.)" , "Yet to be taken to court" .)