A game man runs the show (5)
I believe the answer is:
rules
'runs the show' is the definition.
The definition and answer can be both to do with social activities as well as being verbs in their -s form.
Perhaps there's a link between them I don't understand?
'a game man' is the wordplay.
'a game' becomes 'RU' (rugby union).
'man' becomes 'les' ().
'ru'+'les'='RULES'
Can you help me to learn more?
(Other definitions for rules that I've seen before include "controls" , "In Australia, football" , "Governs; regulations" , "Australian football" , "strips" .)