First, it takes a lot to be a dancer. You have to be very strong, and do exercises and stretches just like in any other sport. You have to be able to move quickly and lightly. If you do several types of dance, maneuver your body in different ways: you have to move sharply (as in hip-hop), or be graceful and fluid (as in ballet and modern). Sometimes you have to do both in the same style of dance!
So you're thinking, it's just a hobby. Have you heard of the New York City Ballet? They literally dance for a living. Dancing, if you really love it, can evolve into so much more than just an activity you sign up for because your schedule is free. It can become your life. Think about it: professional football players have a very large part of their life taken up by football. So why can't dancers have their so-called "hobby" be a large part of theirs? Maybe we should just start saying that Kobe Bryant's position on The Lakers is just a hobby. Hmm? Ohhhhhh, so that's not a hobby, but Tyler Angle's position on the New York City Ballet is. Because that makes so much sense. Is this just a hobby? Oh, maybe this huge, famous show (So You Think You Can Dance) is just for people doing it as a hobby. Oh, and both of the people dancing in that link were boys. Please. Don't even get me started on all of that sexism: "Oh, it's not a sport because girls do it. And boys don't dance." (You'll have to imagine the nasal voice that I'm picturing.)
Have you ever even come close to dancing? If you have, and you still think it's not a sport, read the above paragraphs again. And again. And again. And again. And again. Get the idea? But if you haven't ever tried dancing, why are you developing these misguided opinions on it? (And yes, I have tried basketball, soccer, and floor hockey. Even if they are in gym class, I still know what it is to play them.) I know that I am extremely opinionated. But I'm not saying that 2+2=5. Now that would be debatable. I'm simply stating that, although dance isn't in the Olympics and that it doesn't have many rules, dancers will always be athletes. So, whether you are a football or a basketball player, whether you are Kobe Bryant or a boy who doesn't, and won't, believe me, dance will remain an amazing sport. One of my favorites, I might add.