Belatedly recognizing the potential for tension, Darst attempted to convince the city's TV stations and newspapers to play down the story. The Post-Dispatch buried it, but the Globe-Democrat splashed the news across its front page: "Pools and Playgrounds Opened to Both Races." When the pool opened that afternoon, about 30 black and 200 white swimmers lined up, eyeing each other nervously. As the swimmers entered and played uneasily in the water, maintaining careful distance from one another, a large, unruly crowd of white people gathered outside the gates of the pool, "nearly all of them carrying baseball bats, sticks, and clubs,” according to an oral history of St. Louis in the collection of the city’s Mercantile Library. A half-dozen police officers arrived and began escorting away the black people who were leaving the pool. But they made no effort to disperse the crowd. A few older men began haranguing the teenagers: "You want to know how to take care of them niggers? Get bricks and smash their heads." As evening approached, groups of white people began threatening black people who approached the pool and randomly beating those who were leaving, chasing them and shouting, "There're some niggers!" One besieged black youth pulled a knife and beat a 20-year-old white cement-company worker. Police rushed to his rescue.
By the evening, the crowd had grown to 5,000, swollen by baseball fans arriving for the Cardinals' game against the Giants that night. The riots only got worse—they did not stop until after midnight. Miraculously, no one died—though ten black people and two white people had been hospitalized.
One of the African American swimmers at Fairground Pool that day, Walter Hayes, later recalled, "I never knew that hatred actually traveled in waves. I could feel and see those hate waves, similar to heat waves coming at you on a hot, sunny day in a desert, coming from the crowd. It was an eerie feeling."
Then, and now, the root cause of the violence was segregation. During and after the Depression, thousands of African American families had migrated up the Mississippi to St. Louis. The New York Times editor Gerald Boyd, who grew up in the city, remembered, “Blacks filed off the highways and out of the train depots into slums that were already brimming with new transplants. Jobs were plentiful in huge plants producing everything from beer to bricks, from shoes to steel. But not everyone found work, and in close quarters, crime and illness were on the rise.”
Virtually all of the area's major retail businesses were downtown—retailers had not yet followed the white community to the suburbs—so the center city was the only place to shop. But black people were routinely refused service at the lunch counters at department stores, dime stores, and drugstores. At some places, African Americans were allowed to eat—but only if they were standing up. They called it “vertical segregation."