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.
*off one's game
Fig. not able to play a sport as well as normal. (*Typically: be ~; put one ~; throw one ~.) I'm a little tired, and that generally puts me off my game.
off (or on) your game
playing badly (or well).