Animals when stopping wagers (6)
I believe the answer is:
beasts
'animals' is the definition.
('beast' can be a synonym of 'animal')
'when stopping wagers' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'stopping' indicates putting letters inside (stopping can mean blocking a gap).
'wagers' becomes 'bets' ('bet' can be a synonym of 'wager').
'as' put into 'bets' is 'BEASTS'.
(Other definitions for beasts that I've seen before include "Basest sort of animals" , "Large four-footed animals or cruel people" , "Large wild animals" , "Fine animals" , "Basset found among other animals" .)