At least four people were injured during the first running of the bulls in the northern Spanish city of Pamplona, organisers said yesterday.
Four men were hospitalised with bruises and contusions.
None of them was gored, they said.
The running of the bulls is a traditional part of the annual San Fermin festival.
The nine-day event – made famous by Ernest Hemingway’s 1926 novel, The Sun Also Rises – honours the patron saint of the Navarra region and draws hundreds of thousands of visitors.
In a test of courage each morning of the festival, daredevil runners armed with nothing but folded newspaper run ahead of 600kg bulls on an 825m track.
The animals that are let loose on Pamplona’s narrow cobbled streets, are then driven to a bullring, where they are later killed in an evening bullfight.
While hundreds of runners are injured every year, stampedes are rare.
Fifteen people have been killed in the bull runs since 1924.
The most recent fatality was gored to death in 2009.
The event, which has become controversial in Spain and is being protested by animal welfare groups, still brings countless numbers of tourists from elsewhere in Europe, Australia and the United States.