Port in northern Massachusetts, beer in southern Massachusetts, initially (5)
I believe the answer is:
salem
'port in northern massachusetts' is the definition.
'beer in southern massachusetts initially' is the wordplay.
'beer' becomes 'ale' (I've seen this before).
'in' indicates putting letters inside.
'initially' indicates taking the first letters.
The initial letters of 'southern massachusetts' is 'sm'.
'ale' inserted within 'sm' is 'SALEM'.
(Other definitions for salem that I've seen before include "where possessions were claimed?" , "New England city, site of 1692 witchcraft trials" , "Massachusetts city, scene of witch hunt" , "Western state's capital" , "holy city" .)