I assume while you were coaching, the kid was severely drugged up...Wonder what he was like without the drugs...
Sometimes (but not in all) I think symptoms can be taken care of by changes in diet. My six year old will not focus at times and would probably seem like he has ADD, but those are the times we know he has had too many carbs or sugar and needs more protein.
Not always... There were some games where his dad would stop by to tell us that his son was having "a bad day", which I always took to mean that he didn't take his meds that day.
Not to judge someone else's parenting, but I could never understand how they could drop him off to us like that and go sit in the bleachers and let us deal with it. Occasionally when things got really wacky, his father would come into the dugout and sit with him, but rarely.
He was certainly not a bad kid - there was never any issues with him getting along with the other players - he mostly interacted with the coaches and his communications skills were kind of poor. It was mainly an issue of focus, which is always an issue with at least 2 or 3 kids on any team I have coached, but his was the worst case I ever saw.