Young men in jeans or shorts and t-shirts chased the 580-kilogramme (1,280-pound) beast, named Vulcano, through the fortified town of Tordesillas in central Spain.
It was slaughtered after crossing a bridge into a meadow where it faced crowds of people, some on horseback and many carrying lances.
A total of 12 people were injured in the event, known as Toro de la Vega, a Red Cross spokesman said.
Most people suffered cuts and bruises but two people had broken bones and one person was gored: photographer Pedro Armestre, 41, a freelancer who works regularly for news agency AFP and was covering the event for the agency.
The bull gored Armestre in the right thigh.
Armestre, who was conscious and speaking to AFP's Madrid office after the injury, was taken to a hospital in Valladolid for surgery.
The Red Cross official said Armestre's condition was serious but not life-threatening, describing the skewering as "long but not too deep, that is to say, it is not an excessively serious goring".
Hundreds of activists from the Party Against Bullfighting and Animal Cruelty (PACMA), protested in Madrid three days ahead of the event. Banners at the protest declared: "Torture is not culture" and "Stop Toro de la Vega".
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Activists from the group delivered a petition to Spain's parliament, saying it contained more than 85,000 signatures opposing the Toro de la Vega.
Tordesillas' mayor Jose Antonio Gonzalez Poncela played down the protests, saying there were similar demonstrations at bullrings around Spain "so it is nothing more than that".
"There are always people in favour and people against in all aspects of life, not just for bullfighting," he told Spanish public radio RTVE.