Says, by the way, it's the wrong seat (6)
I believe the answer is:
states
'says' is the definition.
(state can mean to say or declare)
'by the way it's the wrong seat' is the wordplay.
'by' is a charade indicator (letters next to each other).
'the way' becomes 'st' (abbreviation for street).
'it's the wrong' indicates an anagram.
'seat' anagrammed gives 'ates'.
'st' put next to 'ates' is 'STATES'.
(Other definitions for states that I've seen before include "Conditions of American administrative units" , "Announces" , "Conditions or circumstances" , "They're united in America" , "Administrative units in America" .)