I have seen injuries in sports from many different angles. When I played, I broke some one's leg, I broke ribs,and in my first game a kid did a head first tackle and had to be carted off with some type of neck injury. Someone that worked at the park said something like "so this is your first game, I hope it doesn't scare you away from it." And now I am a paramedic and I've seen about every type of bone break (nice big open ones) and its amazing some people's tolerance and the body's ability to cope.
Head injuries are a very scary thing if you don't know much about them, here's a few articles about head and neck injuries in football and other sports, it has some good information about mechanisms of injury
http://www.medco-athletics.com/body/Free-CEU.htm this also could help you in penalizing certain "head tackles."
Also This is a question for any other health professionals who also officiate. When and how do you or should you intervene/take command of medical situations during contests you are officiating? This may also extend to the stands in some cases where you have a low-level, rural, not well staffed game. I haven't really had to be in any of these situations, but I'm bound to be in someday, especially officiating 4 sports, so I'm looking for anyone who has been there.