Ordinary people have a bet about it (5)
I believe the answer is:
laity
'ordinary people' is the definition.
(I've seen this before)
'a bet about it' is the wordplay.
'a bet' becomes 'lay' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'lay' enclosing 'it' is 'LAITY'.
'have' acts as a link.
(Other definitions for laity that I've seen before include "Non-clerics" , "Unordained people" , "Lay people" , "Laymen" , "They're not the clergy" .)