Of course a lot of this is only my personal experience and I know I've reiterated some points other people have made, but like Jeremy said, sport is rarely if ever considered a waste of time by the participant. Work generally always is and I think the fact that it can prevent you from devoting the time to your chosen sport/s that you would like is perhaps the point these people who criticize you.
You are obviously a very active person and therefore not lazy in a physical sense as already mentioned. But as your critics recognize, if you had a job, your life would be extremely different. You would suddenly have a lot less time to play these sports and its an incredibly frustrating situation to be in. And as already mentioned, I think there is definitely a lot of jealously surrounding the criticisms you have endured. When I was sixteen I was going to school and doing jujitsu 4 days a week, and the biggest thing I had to worry about was a maths exam. What I wouldn't give to be able to have that lifestyle (though maybe not the being sixteen part!)
But on another point, whilst sport imbues you with values such as the rewarding nature of hard work and persistence, work teaches you the value of money. Your understanding of the world and everything around you changes when you realize how much things cost, and how hard you have to work to be able to buy the things you need, let alone the things you want, and perhaps those around you feel as though this is something you would benefit from learning. But if you're only in the tenth grade, there's still plenty of time left for that!
Enjoy your sport and play hard, but like Dyalan said, until you have experienced what its like to work a full time job, don't be too hard us working people, even if we tend to whinge a lot!
On a side note though, I'd never consider studying draining. But that might have something to do with the fact that I'm a nerd
