Seems kinda obvious -- any impact that jostles the brain can eventually "add-up" to serious damage. Just because somebody doesn't black-out, or stumble to the ground.........that doesn't mean the brain didn't receive any blunt-force, or vibrations.

One soccer header vs an elbow to the skull -- clearly, the elbow is going to cause more damage.

But let the soccer player take 200 headers per week, for 30 years -- why wouldn't that create some risk?