@Pinkninja I'm a bit late to this thread, but here is my experience. By 15, I was way overweight at 165 pounds and "sports" was playing the olympic games series on the Commodore 64. 3 years later, I was 145-150 pounds, had gained a few inches in height, and was moving much more. In the summer, transportation meant cycling. In the winter, I tried to go to the pool a few times a week and lifted weights (with a poor routine, I wish I had learned the powerlifts at that age, but still, I was in the gym!) . So, how did this happen? Here are in no particular order a few pointers. Maybe they will help.
1 - The good news: losing the weight was incredibly easy. A 17 year old male had the perfect hormonal profile for this. "Diet" consisted in having dessert only once a day and having fries only 3 times a week. Breakfast was the traditional toasts with peanut butter and jelly, I ate at the school cafeteria (then the university cafeteria) on school days and had dinner at home. I ate snacks whenever I was hungry and never counted calories. Yet, I lost 20 pounds in 2-3 years. In fact, I had trouble keeping my weight reasonable. at 6 feet tall, I would sometimes get as low as 140 pounds in the summer.
2 - Exercise: what happened? Well, I undid the damage of high school phys ed. I was really bad at sports as a kid, and was therefore always chosen last when we made teams. I had no talent and the teachers were awful. Example: one day he decided to time a 1 km run and grade us on it. No preparation, no training program, just, OK, let's go to the park, run, and you get a grade. How are people supposed to like physical activity after that? If I recall correctly, math teachers at least try to show you the stuff before the test. They don't say : OK, today we have a calculus test when they never talked about it.
I don't know what your son's experience is with sports and physical activity, but there is a wide range of activities one can do. You are not limited to soccer and basketball. If you don't like sports team, you can try endurance activities. I fell in love with cycling, so that was my activity. However, I also after that, in my 20s, did many individual sports (as opposed to team sports): badminton, squash, fencing, swimming, ... I'm sure there is something your son would enjoy. He must find it. Once I got in good enough shape to do OK, I also started to enjoy team sports and played water polo and rugby, but that is a personal taste. Many people go through life never doing team sports.
2a - My 7 year old daughter has a weight problem. We had trouble getting her to exercise. We however encouraged her any time she wanted to try something. Even at 7 she is stubborn, and coercion does not work that well. This winter she tried tennis, out of her own will, and is now hooked. This was a bit weird as I had played a bit when I was 11-13, but had never mentioned it in front of her. She probably saw some tennis videos on Youtube and found them interesting. We have a park with courts 2 minutes from our house and my wife, daughter and I go on a court and just play together, taking breaks when needed. Sometimes, my daughter will play for 2 hours in a row and cry when it's time to leave because our reserved time is over. She found her physical activity, and is losing weight like crazy (well, in combination with a "diet", but at that age, "diet" consists in only limiting sweets. If she is hungry outside of meals, snacks consist usually of fruits).
3 - Stubbornness and know-it-all-ness: I don't know about your son, but I and all my friends were really stubborn at that age and thought that at 17 we really didn't need anyone to tell us what to do. Ordering him to do sports is likely not to end well. Encouraging him to try stuff may work. The details really depend on his psychology. Stubbornness may be an advantage. Once he catches on with something he likes, he may just go all in with it. If he likes role models, finding an active one he can identify with can be good. If he is more of a rebel, then finding rebel activities (skateboarding, etc...) may work. If he wants to please the ladies, then bodybuilding could be good.
4 - Hormonal profile (part 2): Your son has a one in a lifetime opportunity to build muscle like crazy (well, without using drugs). When I was playing rugby, I kept on seeing kids coming in our club at 16-17 looking like, well, kids, and 3 years later, looking like men and starting to give me trouble at training. All they needed was a lot of food and the coach to give them a nice lifting program to do in the winter. I wish I had known all I know now regarding training and nutrition at 17. If you can subtly get your son to "get" this, depending on his personality, he may just start training on his own.
OK, that is a lot longer than what I expected and I don't have a magic bullet. However, I was like your son when I was 15-16, and now I read this forum, deadlift, snatch kettlebells and play tennis. I would still do water polo and rugby if this old body would follow, but I want to keep whatever is left of my joints for old age. There is a way for your son to get back to a healthier path, and I hope I provided a few helpful pointers.