Right! No, Left!
International Left Handed Sports Day is the time to play every sport and game with your left hand or with left handedness as appropriate.
For example, when batting in baseball, swinging the club in golf, or holding your stick in hockey, you do so as a natural left-handed person would.
When holding a piece of equipment that only takes one hand, such as a baseball glove, tennis racquet, or ping pong paddle, you put it on or in the hand a left-hander would.
Throw a ball only with your left hand today. Basketball is a little tricky here because you can shoot or pass with equal force from both hands. Many times you actually shoot more with one hand than the other, so today that hand must be your left.
The requirements for today also including kicking the ball with your left foot in a game of kickball.
Swing your polo mallet only with your left hand today.
Naturally left-handed people do not have to switch to right-handed activities today. Ambidextrous people do have to go all left today.