My non-CAH son played tackle football from the age of 7 or 8 all the way through high school with no serious injuries except for the broken collar bone he suffered one year.  No other injuries were football related.  Organized football should be well regulated and the kids should be wearing all the protective equipment.  You can buy additional protective equipment as we did - the neck roll, elbow pads, etc.  I would let the coaches know of the CAH and I would be there for practices as well as games if it was my son. 

My daughter who has CAH has played basketball, soccer, softball and now rides horses.  She has taken a few nasty falls from a horse, but we make sure we are prepared with her emergency injection if we should ever need it.  So far, we have never used it at a show.  Her biggest concern was becoming overheated and dehydrated playing team sports, so we took plenty of water and gatorade with us and made sure she was hydrated before she started and could replenish as the games went on.

As my pediatrician and endocrinologist both told me, they are kids and you have to let them be kids - just be prepared for an emergency should one arise.  Good luck.