To penetrate that defensive shell, most teams sacrifice the puck, firing it into the zone in order to win it back amid the thicket of bodies near the net.

WSJ: How the Chicago Blackhawks Became Unbeatable

Crosby didn't score the goal, but he set it up by storming unimpeded into the Islanders' zone, then firing a backhand shot.

WSJ: Penguins End Islanders' Season

Lessons have been learnt, including that a minimum safety buffer zone of 1, 640ft (500m) is established before firing smoke rounds.

BBC: Sapper Mark Smith death: Coroner calls for inquiry