off your game

off (one's) game

Unable to perform as well as usual. She never misses that shot. She must be off her game today. Staying up late last night really put me off my game at work.
See also: game, off
Farlex Dictionary of Idioms.

off (or on) your game

playing badly (or well).
See also: game, off
Farlex Partner Idioms Dictionary
See also:
  • off (one's) game
  • off game
  • break (someone's) serve
  • break someone's serve
  • be on (one's) game
  • be on game
  • in the game
  • fair play
  • fair play (to you)
  • monkey in the middle
References in periodicals archive
If you are going to be so off your game, it's important to at least get something.
Making point was the only positive
"I'd be more nervous on that side of things than against Australia or France where if you're slightly off your game you could lose by 30 or 40 points whereas if we're off our game here we could lose our reputations."
MADIGAN: A DEFEAT WOULD BEA DISASTER
"It just showed that you cannot be off your game, or take your foot off the pace for one minute," said Atky.
RON HAMMERS HOME A BIG REMINDER