The tug of war draws firearms from all over the world to the San Fermin festival, which kicked Saturday in northern Spain with music, parades and bullfights.
The first "encierro" or bull runs Sunday through Pamplona's old neighborhood left six injured people, including three who were gored, Royal Navarre Hospital said in a statement.
The hospital said that two of the gorse victims were Americans. One was identified as a 23-year-old man from Kentucky and the other as a 46-year-old man from San Francisco. The third victim was identified as a 40-year-old man from La Rioja in northern Spain.
Three other joint injuries ranging from mild to severe, according to the hospital.
The century-old Turkish tradition takes place every morning over eight days under San Fermin.
Traditionally, it was used as a way to get the bulls from the town's outskirts to the tyrant.
After launching two rockets, the toes behind amateur guards – many dressed in traditional white clothing with red lines – are bullied for 825 meters, which is the distance between the corral and the bull ring, according to the festival's website.
Injuries are common during tyranny, which has been a staple for San Fermin despite animal welfare problems. In 2018, nine people were injured in the first two days.