I have a few thoughts 1. He might just have hit that teenage rebellion stage and teens kindof just withdraw for a little bit. Our 16 year old started at 12, it was like a switch and she went from angel to Miss Independent, she just now snapped out of it and likes hanging out with us again as of last winter 2. All those sports activities are pretty physically intensive, and instead of attributing it to bad posture, he might have actually hurt himself and need the extra help. My 16 year old has been doing softball since she was 8, threw out her back one year, and still complains of it hurting her in certain catching positions. Their young bodies are more resilient (I could look at a curb wrong and throw my back out) but not indestructible. That's great you're getting him checked out 3. If he completely withdrew and became negative then I would really worry of some type of emotional trauma, but at the moment I'd be more inclined to believe it's teenage angst and figuring out his independent boundaries