American Football. We are the only country to win a super bowl.
I like baseball's WORLD series, where only one country (sometimes two) participates.
I've been advocating for the Korean and Japanese leagues to join in. They are some good competition.
Too bad the Baseball World Cup is no more.
Though to be honest, it feels great to still be able to say that we're world number 1 in Baseball. (Netherlands was the champion in 2011, when it was held for the last time)