Motorists ringing about northern stadium (5)
I believe the answer is:
arena
'stadium' is the definition.
(eg a sports arena)
'motorists ringing about northern' is the wordplay.
'motorists' becomes 'AA' (Automobile Association).
'ringing' is an insertion indicator.
'about' becomes 're' ('re' means regarding or about).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
're'+'n'='ren'
'aa' going around 'ren' is 'ARENA'.
(Other definitions for arena that I've seen before include "Scene of action" , "theatre" , "bowl? Possibly" , "Scene of gladiatorial contest, perhaps" , "domain" .)