On October 30, 2019, the seventh and final game of the 2019 World Series will be played. It's currently 3-3 and the interesting thing is that so far, the away team has always won; the Nationals won the first two games in Houston, the Astros won the next three in Washington and the last game, in Houston, was again won by the Nationals. Playing home is usually considered an advantage; I found an article claiming that it's not (such) an advantage in baseball as in other sports, but that focuses on series instead of single games, and in series the better team is most likely to win anyway.
The Houston Astros may still win the final game on their home turf, but if they don't: would this remarkable feat be a first? Or has there ever been a best-of-seven series where all games were won by the away team? This answer seems to suggest it never happened in the NBA, but maybe in the MLB or NHL, or another major competition with best-of-seven playoffs?