Three up, three down. That's been the story of the NHL series between the Boston Bruins and Philadelphia Flyers. The Bruins won the first three games, then the Flyers came back to win three in a row themselves. Forcing a Game 7 when down 3-0 is exceedingly rare in professional sports. Winning a series down 3-0 is even rarer still. Three teams have ever done it, 276 teams have failed.