Small game: deer? (4)
I believe the answer is:
stag
'deer?' is the definition.
(stag is a kind of deer)
'small game' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'game' becomes 'tag' (children's playground game).
's'+'tag'='STAG'
(Other definitions for stag that I've seen before include "Male-only" , "speculator wanting quick profit" , "This party is for men only" , "Hunted animal" , "Hart" .)