Indefinite number in parish theatre (5)
I believe the answer is:
arena
'theatre' is the definition.
(I've seen this before)
'indefinite number in parish' is the wordplay.
'indefinite number' becomes 'n' (n can represent any number).
'in' is an insertion indicator.
'parish' becomes 'area'.
'n' going within 'area' is 'ARENA'.
(Other definitions for arena that I've seen before include "Battleground" , "Place of combat" , "Playing area" , "Performance space" , "Engagement ring" .)