There is a lot of information at www.cdc.gov/TraumaticBrainInjury about head injuries.
Another good place to learn about Sports and Concussions is: www.cdc.gov/concussion/sports. From here you can get some good information about how to recognize a concussion, what you should do if someone might have a concussion, preventing concussions, and some good things you can print out and keep in your Coaching Clipboard if you are a coach of ANY sport.
The CDC has this great page of additional resources that includes videos about concussions as well as more educational materials.
In October, 2011 the CDC published this report about non-fatal traumatic brain injuries (i.e., concussions) in children under 19 years old. It is interesting to look at the bottom of the report where there is a table about the five most common activities associated with ER visits for concussions, split up by age and sex.
There is some more information at the KidsHealth.org site on concussions and other sports related injuries at http://kidshealth.org/teen/safety/first_aid/concussions.html
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