Short head not turning in US city (6)
I believe the answer is:
boston
'us city' is the definition.
(capital of Massachusetts)
'short head not turning in' is the wordplay.
'short head' becomes 'bos' (I can't explain this - if you can you should give a lot more credence to this answer).
'turning' is an anagram indicator.
'in' is an insertion indicator.
'not' anagrammed gives 'ton'.
'bos' placed within 'ton' is 'BOSTON'.
(Other definitions for boston that I've seen before include "US city; card game" , "Site of rebellious tea party" , "Card game; dance" , "US city of historic Tea Party" , "American city noted for historic Tea Party" .)