This entire article should be read by anybody playing hockey, football, rugby, or soccer. The pressure to continue playing can be very dangerous.

http://www.nytimes.com/2012/11/30/sp...medium=Twitter

An important paragraph says:

"That study found concussion rates seven times higher than previously reported. In the study to be published Friday, the male players sustained concussions at three times the rate reported in most previous studies, and the female players at five times the rate reported in most studies. The women also sustained concussions almost twice as frequently as the men, despite rules in women’s hockey designed to curb body checking. The brain scans taken after the season also showed substantive metabolic changes among the majority of players, including those who were not diagnosed with concussions. Researchers said the changes in the brains might be evidence of trauma caused by subconcussive blows. "