When I went to link in the Russell Wilson extension thread, I came across this:

The Seahawks coaching staff led by Assistant Head Coach/Defense Rocky Seto has updated the tackling video released in 2014 as a way to educate coaches, players and fans outside of the organization about the team’s methods of tackling. The philosophy takes the head out of the play and increases safety, all while maintaining the toughness and physicality that makes the game great. NOTE: Like any athletic activity, no tackling technique can completely eliminate the risk of injury.

http://www.seahawks.com/video/2015/0...hawks-tackling
In short, they're bringing basic rugby fundamentals to football.