The reason? Pooping pigeons.
"Jared [Followill, the band's bassist] was hit several times during the first two songs," said band manager Andy Mendelsohn. "It's not only disgusting - it's a toxic health hazard. They really tried to hang in there."
The birds apparently were in the rafters of the city's Verizon Amphitheatre and began their attack Friday during the band's opening song, hitting Followill, 23, in the face.
"I was hit by pigeons on each of the first three songs," Followill said. "We had 20 songs on the set list . . ."
A statement from the band said, "We want to apologize to our fans in St. Louis and will come back as soon as we can."
The band played in Chicago as scheduled Saturday night.
News reports said fans - who apparently were not affected by the pigeons - will receive full refunds, although officials of Verizon Amphitheatre and the concert promoter Live Nation have not commented.