Good point. Thanks for the correction.
The fact they're finding it in many other sports and in military personnel, as pointed out in the FAQ, makes me pretty skeptical that this is a disease strongly linked to nonconcussive hits since hockey players and soldiers aren't butting heads every day. But it's pretty hard to draw conclusions while the data and definitions are so vague. Do you know if they've looked specifically at populations of long-time football players with no concussions?
A review article from 2012 had this to say
> While it is clear that anyone who suffers repeated head trauma, regardless of the mechanism, may carry the risk of developing CTE, there is no clear consensus on how much or how little trauma is needed to cause CTE. While most feel CTE is a manifestation of repetitive trauma, the question still stands if it can be caused by a single TBI [10]. In a study by Johnson et al., widespread tau and beta-amyloid deposition was found in the brains of individuals who suffered a single traumatic brain injury. The study included the examination of postmortem brains from long-term survivors (1–47 years) of a single TBI () versus uninjured age-matched controls (). Results showed NFTs to be exceptionally rare in young uninjured controls, yet were abundant and diffuse in one-third of TBI cases.
http://www.hindawi.com/journals/rerp/2012/816069/
The last sentence seems to support the idea that the appearance of symptoms is an important threshold, but it's hard to tell what they mean; could also be that anyone cracking heads enough to get sub-concussive CTE are likely to have picked up at least one full concussion.
> I'm a big guy and I live in the south, so you can bet I played my share of football growing up--there are definitely a lot more repeated hits to the head in football than any other popular youth sport
I played 11 years of football, mostly on defense and mostly with my head, and I fully agree. I coach youth football, so any data that would show a dramatically higher risk for football than other sports (which are generally regarded as acceptably risky) is of great interest to me.