Thousands of thrill-seekers ran with the bulls on a crowded fourth day at the San Fermin festival in Pamplona on Sunday. Ten people were injured but no one was gored.
Several runners tripped, fell and were trampled as crowds raced alongside the massive bulls of the famous Miura breeding estate, founded in 1849.
The Sunday run is usually the biggest of the eight that take place annually and is particularly favored by aficionados because it traditionally features Miuras, renowned as Spain's largest fighting bulls.
Navarra Hospital reported in a statement that 10 people received treatment for minor injuries including arm and head trauma. Nine of them _ all Spaniards of ages ranging from 19 to 41 years old _ were kept in for observation.
Pamplona experts at state television TVE said around 3,500 people had run with the bulls on Sunday.
One runner slipped and fell in front of the bunched herd and was trampled near the beginning, a second one tripped close to the halfway point and was seen to be hit by several flying hooves, and a small group jostled each other and hit the cobblestones as the bulls neared the bullring.
The run covers 928 yards (850 meters) from an enclosure just outside Pamplona's medieval stone wall, where the pedigree animals spend the night, to the downtown bullring where fights known as "corridas" take place each afternoon of the festival in honor of the city's patron saint.
Sunday's run was quick at 2 minutes, 29 seconds and would have finished even sooner but for one straggler that looked around and charged at several herders in the ring before being guided into a corral.
The largest Miura was a black specimen called Macareno that weighed 695 kilograms (1,532 pounds) while the lightest tipped the scales at a mere 540 kilograms (1,190 pounds), the games and spectacles branch of Navarre regional police said in a statement.
Despite the animals' size and musclebound appearance, experts admire Miuras for their explosive acceleration, stamina and grace, characteristics that inspired legendary Italian car maker the late Ferruccio Lamborghini to name one of his iconic sports cars after the breed.
Harold Heckle in Madrid contributed to this report.