tackle football. He has never been injured and I can count on one hand how many times over the years any player on his team has had any type of injury, let alone head injury. My oldest has always been one of the 2-3 lightest players on his team. Because he has been playing and has learned how to tackle safely, he isn't afraid and I believe his chances of getting hurt are much lower.
The kids that start playing at age 11-12 or later may have a disadvantage because they haven't learned how to tackle yet and are not used to the contact. I think it increases their chances for getting hurt. Even the best athletes in this age group struggle to catch up in that area.
I was the head coach of my younger sons 7-8 year old team last season. I remember one kid on another team getting injured last year, but other than that, no injuries for our team or any of our opponents all year. The speed of the game is pretty slow and the opportunity for big hits is very small. I've seen more injuries in my kids soccer games than I have in football so far. Of course I do expect more injuries as the kids get older and the game gets faster. I am concerned about it but our family loves it and it has been great for their discipline and confidence so far.