Any game played with a ball. / A specific contest or match between teams playing such a game, in particular a baseball game.

(idiomatic) A foolish, profitless, or hopeless undertaking.

Any of several confidence tricks in which something worthless is substituted for something of value, often in a sealed envelope.

Any of various children's games where participants form a ring or circle, often with hands joined.

(poker) A game where the chips directly represent money and players are free to leave at any time, in contrast to a poker tournament.

(informal) An attempt to psychologically manipulate or intimidate someone. / A mental pursuit or obsession. / Skill at fellatio.

Alternative form of head-game

(sports or figuratively) Critical and having the potential to alter the overall outcome.

simple past tense and past participle of game the system

To use the rules and procedures meant to protect a system in order to instead manipulate the system for a desired outcome.