Clue: Everyman's retreated inside, mean Northern heavyweight wanting a game (9)
Answer: BADMINTON
Explanation: Definition: game
An envelope ('inside') of MI, a reversal ('retreated') of I'M ('Everyman's' – ie. Everyman is) in BAD ('mean') plus N ('Northern') plus TON ('heavyweight'). 'Wanting a' does not serve much purpose, unless 'mean' is BAAD.