A gang losing wide piece of territory (4)
I believe the answer is:
acre
'piece of territory' is the definition.
'a gang losing wide' is the wordplay.
'gang' becomes 'crew' (synonyms).
'losing' suggests deleting specific letters.
'wide' becomes 'w' (abbreviation e.g. in cricket).
'crew' with 'w' taken out is 'cre'.
'a'+'cre'='ACRE'
(Other definitions for acre that I've seen before include "Not a lot of land" , "region of ground" , "Persistent tendency" , "Middle East port" , "Unit of land area" .)