Okay kiddo, so nationalism means people feeling really proud of the country they come from. And sometimes, when their country's sports teams play against other countries' teams, those feelings get even bigger!
So imagine you're playing a game of tag with your friends, but instead of just tagging each other, you're also representing your whole country. That's kind of what happens in sports like soccer, basketball, and the Olympics. People from different countries compete against each other and try to be the best.
Now, when people from one country watch their team play against another country's team, they might get really excited and cheer really loud. That's because they want their team to win and show everyone that their country is the best at that sport.
Sometimes, people might even wear clothes or wave flags with their country's colors on them to show their support for their team. And when their team wins, people might even have big celebrations!
So, sports can bring out the feelings of nationalism in people because it's a way for them to show how much they love their country and how proud they are to be a part of it.