When Canadian and American teams are playing each other, it is tradition in the NHL for the arenas to sing both country's national anthems. In this case, they sang the Star spangled Banner first, as the Panthers are the visiting team. As the anthem singer started the American tune, many of the fans in the crowd started chanting, "Sergei, Sergei," in an attempt to get inside the head of the Panthers netminder.
When asked how fans felt about this, the response was rather unified. Oilers fans collectively pointed out that Panthers fans booed in Florida when they were singing the Canadian National Anthem, O Canada.
This does not necessarily make chanting during the American National Anthem acceptable. After all, two wrongs does not make a right. That being said, at the end of the day, this doesn't really matter. The Oilers lead game six 2-0 early in the second period as they attempt to become just the 10th team in NHL history to force a game seven in a series after going down 0-3. Tune in yourself to see how the rest of the game plays out.