Neighbourhood which includes Newcastle’s foremost stadium (5)
I believe the answer is:
arena
'stadium' is the definition.
('arena' can be a synonym of 'stadium')
'neighbourhood which includes newcastle's foremost' is the wordplay.
'neighbourhood' becomes 'area' (I've seen this before).
'which includes' is an insertion indicator.
'foremost' indicates taking the first letters.
The first letter of 'newcastle' is 'n'.
'area' going around 'n' is 'ARENA'.
(Other definitions for arena that I've seen before include "Place of public contest" , "Venue for contests" , "Earls Court?" , "Enclosure for sports etc." , "Place for public events" .)