Laughing - Just a guess here, but do you think maybe S's acting up was because he felt guilty about plans to go live with his Dad? You know how WASs start picking fights when THEY feel guilty.
I also wondered if maybe your S didn't go with his dad out of some misguided attempt to save dad or shelter you and your D from him (as in, if I go with him maybe he'll let up on mom?). It does seem odd that he would want to leave football, although your guess that he could be experiencing depression might be right.
Either way - for now, just be cheerful and positive with him. If he won't take your calls, then email him. Validate - tell him you love him and you understand how important it is to teenage boys to be with their dad sometimes.
