Indefinite number leaving stadium in locality (4)
I believe the answer is:
area
'locality' is the definition.
(thesaurus)
'indefinite number leaving stadium' is the wordplay.
'indefinite number' becomes 'n' (I've seen this in other clues).
'leaving' indicates named letters should be taken away.
'stadium' becomes 'arena' ('arena' can be a synonym of 'stadium').
'arena' with 'n' taken out is 'AREA'.
'in' acts as a link.
(Other definitions for area that I've seen before include "land" , "Surface measurement" , "District; locale" , "Space occupied by something" , "Extent of a two-dimensional surface" .)