Sports

Why do we say 'sport' when what we're actually talking about is a 'game'? A game is something which is played, i.e. is not serious. If it is not serious, then, why do people take games so seriously? I say 'serious', when 'hysterical' or 'manic' might be more appropriate words. I wish that people could be just as excitable about important matters. I don't understand.