Your kids don't need you shouting at them on the playing field, any more than they need you shouting at them in the classroom. Let them play the game and figure out for themselves how they feel about it, without having to worry about your feelings, too. Make it clear that your happiness doesn't depend on the score. Cheer for your kid, sure, but do it cheerfully. If you can't manage that, take a walk; the game will go on fine without you, because it's not about you.