Vault over large area's fair game (7)
I believe the answer is:
tombola
'fair game' is the definition.
(game played at a fair)
'vault over large area's' is the wordplay.
'vault' becomes 'tomb' (I've seen this before).
'over large area' becomes 'ola' (this might be a standard abbreviation I've not previously seen).
'tomb'+'ola'='TOMBOLA'
Can you help me to learn more?
(Other definitions for tombola that I've seen before include "Game played at fetes" , "Lottery game" , "Lamb too (anag) - game with prizes" , "Game often found at fetes" , "Ticket-drawing game" .)