B., you said you really didn't need advice, as you knew how you were going to handle this? You say that how you have handled it so far, is not right. I do not know what your intentions are but I would like to try to help, if I may, of course.
You can take it, or leave it, but here is my advice. First, I would like to give you a little history about my experience. My son, who is absolutely incredible at every thing he begins, including sports, computer literacy, intelligible subjects and books; you name it; he is above-average. He would excel in athletics, running, swimming, basketball, gymnastics; everyone loved him and expected him to be in the Olympics. Originally, that is where his heart was. But at some point, he changed his mind, and in his Junior year of high school, after having scouts follow him, he begin to act differently. He did not show passion in most things he did, regardless of what it was, and after a period of time; he was sickened to come to me and ask, "Would you be mad at me if I quit basketball?" Well, of course, in my youth, I was unstoppable too. I excelled in all sports, regionals and state in track, nationals in softball....etc. But I asked him, "I thought you loved basketball, always talking about your victories and all, why would you want to quit?" It was then that I found out; he was only doing these things to "bring me joy and happiness and make me feel proud" of who he is. So that, brought me joy, and I allowed him to be "WHO" he was, which makes him who he is today. We can only guide them the best we can, but we cannot make them who they will be. So I ask you, dig deep inside, and ask yourself if your child is trying to make you enjoy who they are? Trust me, sports does not make the person; it may "help" on a resume for some, but to others, it may display more energy in physical aspects which eventually loses strength, versus wisdom and knowledge, which lasts an eternity and keeps growing within us. Also, I understand the necessity for exercise and keeping fit; I STILL exercise daily to maintain my weight, and it is STILL a constant struggle, but your child can exercise in so many ways.
Be there for your 17 year old, it sets the relationship with them, after they leave home to be an adult. Be proud of them and love them, no matter what. You know the Bible says to love your child; teach and train them up right in the ways of the Lord, and they will not depart from it. That means that no matter where they head in life, they will always have the truth in their hearts because it has been planted there, and no matter how far they deter from the path, God promises to be faithful to our children for a 1000 generations. So be at peace and know that you cannot lead them, but He will.
I hope you take this to heart and know that I am not judging you, but we are to protect them from harm, not our dreams for them. Pray, pray and pray some more for God's will for them.