be on (one's) game

be on (one's) game

To perform with great skill in an activity or pursuit, such as a game, sport, or specific task. I can't believe I missed that catch—I'm just not on my game today. He's getting crushed in the debate tonight. You can tell his opponent is on her game.
See also: game, on
Farlex Dictionary of Idioms.

be on (one's) game

To play a sport with great skill.
See also: game, on
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • be on game
  • in the game
  • be game
  • choose up
  • choose up sides
  • away game
  • fair play
  • fair play (to you)
  • monkey in the middle
  • a shell game