Defenceless woman's right by the sea (7)
I believe the answer is:
unarmed
'defenceless' is the definition.
('unarmed' can be similar in meaning to 'defenceless')
'woman's right by the sea' is the wordplay.
'woman' becomes 'una' (**).
'right' becomes 'r' (common abbreviation).
'by' is a charade indicator (letters next to each other).
'the sea' becomes 'med' (abbreviation of Mediterranean).
'una'+'r'+'med'='UNARMED'
(Other definitions for unarmed that I've seen before include "Maunder along without weapons" , "Not equipped with or carrying weapons" , "Maunder (anag.)" , "Having no means of defence" , "having lost certain members" .)