Teens seen running wild in US state (9)
I believe the answer is:
tennessee
'us state' is the definition.
(state of the USA)
'teens seen running wild' is the wordplay.
'running wild' is an anagram indicator.
'teens'+'seen'='teensseen'
'teensseen' is an anagram of 'TENNESSEE'.
'in' acts as a link.
(Other definitions for tennessee that I've seen before include "Memphis's state" , "Nashville's state" , "Volunteer State" , "16th US state" , "Williams, say" .)