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

"We could have played even better. It was just a game of errors."

From BBC

With an apology to his wife and me, he hurried upstairs and in a minute we heard a game of hide-and-seek going and the shrill laughter of two children.

From Literature

“Like a game!” we’d tell each other: “a race to beat our own record!”

From Literature

The close final tally masks a game where Venezuela seemed to always be threatening to score.

From Salon

The Fed meeting shouldn’t be a “game changer” for the euro versus the dollar, Danske Bank’s Sofie Liv Petry said in a note.

From The Wall Street Journal