One of the leading causes of head injury is body checking from behind. Due to the danger of delivering a check from behind, many leagues, including the NHL have made this a major and game misconduct penalty (called "boarding"). Another type of check that accounts for many of the player-to-player contact concussions is a check to the head resulting in a misconduct penalty (called "head contact"). A check to the head can be defined as delivering a hit while the receiving player's head is down and their waist is bent and the aggressor is targeting the opponent player's head.