WASHINGTON — Hours before the World Series officially returned to this city for the first time in 86 years, the roiling red waves rolled in.

From the Metro, on foot, from their cars and on bikes and scooters, they came in their red Nationals caps and shirts, swarming toward Nationals Park. They came in red jerseys of current stars but also of past ones, a nod to the beloved players not around long enough to play a role in this October miracle.

And among those red waves were bright blue sharks — actually people in shark costumes, which only makes sense if you know the backstory. Nationals outfielder Gerardo Parra’s walk-up song is “Baby Shark,” the catchy children’s tune that has become the Nationals’ unofficial fight song and, in turn, the city’s new theme song.