Losing ground, ground in part of New York (4,6)
I believe the answer is:
long island
'part of new york' is the definition.
('Long Island' is part of 'new york')
'losing ground ground in' is the wordplay.
'ground' indicates anagramming the letters (grind the letters ).
'ground' becomes 'land' ('land' can be a synonym of 'ground'**).
'in' is an insertion indicator.
'losing' is an anagram of 'ongisl'.
'ongisl' going within 'land' is 'LONG ISLAND'.
(Other definitions for long island that I've seen before include "part of America" , "patch cut off in New York" , "Part of New York" .)