People were preparing to enjoy the music of Sugarland live in Concert at the Indiana State fair on August 13th, 2011 when a line of thunderstorms went through and took down the stage. This video from a person in the concert grandstands shows the line of storms going through and the stage collapsing with screams being heard. Dozens were injured at this concert by the stage collapse.
UPDATE; 4 CONFIRMED DEAD
It is for this reason that large events, and even businesses with large numbers of people need to have plans in case of severe weather. Where they plan to evacuate people, how they will do it, and how they will get the warning. This many people getting hurt is a failure of emergency management.