The best thing about sport is the feeling of community. When you cheer for your country, you know that you're cheering with hundreds of thousands others. There's a shared hope, and then either a shared delight or despair.
That's on a wider level. One of the other ways in which this works is on a more micro level when you can share these experience with friends, family and loved ones. Not just the events themselves but also the events around them - the travelling to and from, the anticipation before an event and the analysis afterwards.
It's nice when you find someone new to share this with. A colleague in work also likes American Football, someone in school will too get up at 7:00 to watch Formula 1, a new girlfriend will travel to Dublin to go boxing with you.
These people make enjoying sport possible. Matches, fights, games and races watched alone lack the communal element. Cherish these people. Don't be alone. It's no fun.
