not a parent, never will be.
BUT, knowing what we do know about head injuries I would have to say "no".
Its just not worth it. Not the injury sports. Yes, kids today absolutely need physical activity and they do need to learn teamwork and all that stuff, but there's enough activities out there which aren't going to risk brains and skulls and they can also be fun.
So yeah, in fantasy land where I have a wife and kid, I would not let them do the high impact sports, but I would demand they do some kind of activity that keeps their heart going and keeps them from getting lazy and fat. Also anything that teaches teamwork and social skills is a good idea. Now more than ever.