If I'm reading your post correctly, then rugby concussions occur 1X per 1000 playing hours while NFL concussions are double that rate. Curious what the rate is in college football, as being concussed gets easier after the first time. Believe me, I know. I gave up collegiate play in a non-football sport for similar reasons as Borland and now this center for Michigan. At any rate, assuming this statistic is accurate, I wonder whether one of the of the primary factors is the helmets worn in football. Though accurate record keeping is doubtful, it would be nice to know the concussion rate prior to football's transition away from the leather helmet.