What the fuck kind of football do you play? People don't get dropped on their heads, per se, but they do land on their necks unprotected a lot. Backyard football is just as dangerous as backyard wrestling, if not more so. Backyard football has no pads, no helmets, no mouthguards. When backyard wrestlers wrestle (unless they're the true idiots that use ladders and lighttubes), they're wrestling with the intent of making sure the other person doesn't get hurt; in backyard football, things are much more rough and tumble. When you're wrestling, you can pretty much tell what your friend is about to do to you and therefore prepare for it; in football, they're gonna tackle your ass and you don't know HOW you're going to land. I've had more injuries SLEDDING then wrestling with my friends.
In an addendum, don't you think that a lot of the wrestlers that are popular today got their interest peaked by wrestling in their basement or backyard? Jeff and Matt Hardy are givens for this and there's plenty of others.
As long as people aren't being retarded and trying to put each other through tables or breaking lighttubes over each others' heads, I don't see a problem with it. Backyard football and wrestling aren't really any different from each other.