Many times players who receive concussions in the NFL are playing the very next week. I am not sure, but I believe A Haynesworth came back the very next week this year, and there are most likely others. In the NHL, due to league rules, they must be symptom free for 7 days. After a concussion there are usually symptoms of it for the next few days, so that normally keeps an NHL player out for at least 10 days. I am not saying one sport is more violent than the other or that one rule is better than the other, but there are definitely huge differences in NHL & NFL league policies. The NFL does take it seriously, but they are way more lenient.