Why Was Bruin's Chara Not Disciplined for Devastating Hockey Injury?

Bruins defenseman Zdeno Chara "checked" Canadien Max Pacioretty into a glass partition on Tuesday, leaving Pacioretty with a non-displaced fractured vertebrae and a severe concussion. Pacioretty was chasing a puck along the boards when Chara, who was skating in the same direction, pushed him into the boards. Pacioretty's head struck a glass partition that separates the team benches. Pacioretty had already moved the puck forward, and Chara therefore improperly hit the Canadien. Pacioretty did not move for several minutes, and had to be carried off the ice in a stretcher.
Chara received a 5 minute major penalty for interference and a game misconduct (suspended for the remainder of the game). Although interference (impeding the progress of another player who is not in possession of the puck) is normally a 2 minute minor penalty, a referee may assess a major penalty based upon the "degree of violence."
It is difficult to determine from the video whether Chara intended to injure Pacioretty, although Chara is not known as a dirty player. The NHL determined that there was no intent to injure, and will not discipline Chara. Some have criticized the NHL, noting that there was a history between the two players. Earlier in the year, Chara thought Pacioretty excessively celebrated a game winning goal, and threw punches at him. Chara and Pacioretty were also involved in a fight in a February game. However, fighting and bad blood is a part of hockey, and this incident appears to be more of an improper hit in an unfortunate location. Had the partition glass not been there, Pacioretty would not have suffered the injuries he did.
In most states, athletes assume the risk that they will be injured in competitions, as long as the injury results from ordinary risks that are inherent in the sport. Where the injury results from unique conditions not normally associated with the sport however, participants can be held liable both in civil and criminal forums (see Todd Bertuzzi)
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