A recent class action lawsuit filed by several former NHL players alleges that the league knew about the risk of brain injury associated with playing hockey and, yet, did not do enough to prevent head injuries. Included in the allegations is the claim that, in 1997, the league undertook a study of the issue, but then dropped the ball and did not follow through on what it learned. Only in 2010, when the league implemented the "head check" rule, did the league do anything meaningful to prevent head injuries.