High winds swept through a beer tent where 200 people gathered after a game, killing a man and seriously injuring five others.
But the owner of the St Louis, Missouri, bar that hosted the crowd at the St Louis Cardinals Major League Baseball event said it was lightning that caused the death.
Seventeen people were taken to were hospital and up to 100 people were treated at the scene after winds whipped through a large tent outside Kilroy's Sports Bar, near Busch Stadium.
The crowd was celebrating after the Cardinals had beaten Milwaukee 7-3, a game that ended about 80 minutes earlier.
Eddie Roth, director of the St Louis Department of Public Safety, said winds of about 50 mph shattered aluminium poles that held up the tent, south of the stadium. The force of the wind blew the tent on to an adjacent railway bridge.
Neither Mr Roth and Deputy Fire Chief John Altmann could not confirm a cause of death for the man killed. Mr Roth said he appeared to be in his 50s.
"It was crazy, scary," said Annie Randall, whose family owns Kilroy's. "We're just so sorry this happened." Meanwhile, Janece Friederich was in the car park at Kilroy's when she saw dark clouds approaching. Before she could get out of the car and go into the bar, she saw the tent fly into the air. "It looked like it just got ripped out because it ended up 100 feet in the air on top of the railroad tracks," she said.
Kilroy's owner Art Randall described a short burst of a storm - perhaps five seconds, he said - with a massive wind that lifted the huge tent, threw it high into the air and sent the poles and nearly everything in the tent airborne. When he heard the boom, he initially thought a train had derailed into the tent.
As the wind blew, a bolt of lightning crashed into the bar, Mr Randall said. He said firefighters told him it was a lightning strike, not flying debris, that killed the man.
About two hours after the incident at Kilroy's, tornado sirens blared throughout the city after a funnel cloud sighting. There were several reports of tree damage, power lines down and damage from hail that in some parts of the region was reportedly as big as tennis balls. By late evening, about 2,600 Ameren UE electrical customers were without power in the city.