A game

American  

Or A-game,

noun

Informal.

1. a person’s best effort, abilities, or achievement.

   The candidate brought her A game to the debate.

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'A' game British  

noun

1. informal one's best possible performance, esp in the phrase to bring or take one's 'A' game

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Etymology

Origin of A game

In reference to a sports contest, with the letter A indicating peak performance

Example Sentences

Rangers are second, two points above Celtic, who have a game in hand.

From BBC

“They should also have a game plan for what they would do if the relationship were to end,” Nix adds.

From The Wall Street Journal

In a game designed to erode your sense of reality, the salmon becomes something solid.

From Salon

About finding one small, reliable pleasure in a game designed to strip everything else away.

From Salon

Against the world number seven in Mexico, Boulter won the first set in 28 minutes without dropping a game.

From BBC