One outgrowth of this kind of carelessness was the rise of opportunistic thieves who especially targeted security complexes because they know people living there were, ironically, so utterly unconscious of security once they were inside the perimeter of the keep.

CNN: Pistorius, and the psychology of walls

But after a season-long spike in goal-scoring, teams figured out that if they dropped their skaters back on defense quickly, making the middle of the ice as crowded as a Times Square subway platform, they could keep opposing players on the perimeter of the rink.

WSJ: How the Chicago Blackhawks Became Unbeatable