> That argument, however, doesn't actually square with reality. Rugby, as it turns out, has plenty of problems with head injuries. According to one study, in South Africa about 14% of high school rugby players and 23% of professional and club players annually are diagnosed with concussions. Further, Michael Keating, the medical director for USA Rugby, says that a review of the scientific literature indicates that the number of incidences of concussions among rugby players and American-football players are similar.

From: http://www.time.com/time/nation/article/0,8599,2027053,00.ht...

Rugby (Union) does not have the same incidence of head on head clashes which is what the article focuses on.

The mouthguard is actually the key safety gear for reducing the likelihood and severity of concussion injuries. The soft headgear sometimes worn is primarily for protecting the ears during the breakdown and scrum.

Rugby rules are orientated around 'safe tackle' (eg no above the waist).

The defensive side of American Football is very much brute force orientated especially for the larger players.

Unsubstantiated, un-sourced theory: football players are helmeted, and that helment makes them feel as if 1) they are risking no head damage to themselves, and 2) there is no risk of head damage to others. Thus, lots and lots of targeting of the head and/or usage of the head as a lead component in making or breaking tackles.

On top of that being probable, players try to hide concussions (resulting in compounded head injuries the next time), and players rebel against the NFL's attempts to legislate fewer dangerous head-related hits and tackles. Actually, even fans and the media have the tendency to pine for skull-crushing, cringe-inducing hits at high-velocity.

I could probably have summarized the problem in one word: "culture".