Teens seen running in a state (9)
I believe the answer is:
tennessee
'state' is the definition.
(I know that Tennessee is a state)
'teens seen running' is the wordplay.
'running' is an anagram indicator (the letters run around to different places).
'teens'+'seen'='teensseen'
'teensseen' anagrammed gives 'TENNESSEE'.
'in a' is the link.
(Other definitions for tennessee that I've seen before include "Name of US dramatist" , "playwright's assumed first name" , "Nashville's state" , "Volunteer State" , "... Williams, and southeastern US state" .)