Athletics are generally met with either great enthusiasm or great dread, there's seldom anything in between. What is it about sports that make people want to do them, though? It can't be the attention or highly under-appreciated sports like wrestling and cross-country would have gone the way of the dinosaurs many years ago. My answer would be that it is the learning experience. I'll be speaking from the perspective that I'm most familiar with, that of wrestling, cross-country, and track.
The physical aspect of learning a sport is the most obvious, but also one of the greatest aspects to be had from sports. You learn what your body is capable of. You learn how to take care of it. In cross-country and track, you learn just how far and fast your legs can carry you. In wrestling and boxing, you learn how to defend yourself and be aggressive when it's necessary. The physical aspect of learning in sports is also the aspect that has the most written about it, so I won't dedicate much time to it.
Discipline is one of the greatest things that you can learn from a sport. You're forcing yourself to get up early and go to practice, forcing yourself through the pain in your legs to run those extra miles, and forcing yourself to eat less in order to make weight. You're repeating the same moves over and over until perfection is achieved so that you can be better than your opponent. Discipline is something that you'll require of yourself and that your coach will require of you. It's just that way in life. Being a student-athlete gives you a chance to learn it early and to enjoy yourself in the process.
Respect is also something that you learn from sports. Wrestling and cross-country are particularly good at teaching respect. If you disrespect a coach, you're probably going to regret it. Whether it's being kicked off the team, running until you puke, or doing push-ups until your arms are numb, you'll learn respect for your coach at the very least. Next comes respect for your teammates, who have to endure the same pain that you do day after day. Last is respect for your opponents. If you're acting disrespectful to your opponent before a match, that same opponent is going to get angry and do as much as possible to hurt you. It's that way outside of sports too. You learn to respect those who you've beaten because of how much work they put in, just to fail. You learn to respect those who beat you because you know how much harder they worked. You're familiar with all of those extra miles and all of those extra practiced moves.
The point is that you'll learn things in sports that will help you through life and to be in better shape for any trouble. Through the pain of it, you'll have a lot of fun. So, I would encourage every student to try at least some form of athletics. It's certainly an experience.