They're sports that are kind of like fighting. Just with special equipment and rules to make sure nobody gets more than a few bruises.

[Before it was gifts and cards, and now he has to explain boxing. Well, today's your lucky day, Vanitas. It's time to learn about more nice things.]

Like for fencing, none of the swords are sharp, and you wear a helmet and a padded uniform. And instead of actually stabbing someone, you get points when you hit them.