Last Updated Jul 9, 2014 1:29 PM EDT
PAMPLONA, Spain -- An American who co-authored the book "Fiesta: How to Survive the Bulls of Pamplona" became one of their victims Wednesday when he was one of two men gored at the festival.
Bill Hillmann, a 32-year-old from Chicago and a longtime participant in the nine-day Pamplona street party, was gored twice in the right thigh during one of the daily bull runs, organizers said on their website.
The injury was serious but not life-threatening, the Navarra regional government said in a statement.
A 35-year-old Spaniard man from Valencia was also in serious condition after being gored in the chest during the same run on the festival's third day, the statement said. He was not named.
Photographs showed Hillmann - dressed in the San Fermin event's traditional white with a red neckerchief - being gored on the ground by a black bull as other runners scattered.
Tension spiked when the bull became separated from the pack in the final stretch.
British writer Alexander Fiske-Harrison, one of Hillmann's co-authors of the Pamplona book and a fellow runner Wednesday, said on his blog that the bull turned back and charged at runners.
The six fighting bulls run along a 930-yard course from a holding pen to Pamplona's bull ring in a tense and dramatic few minutes immortalized in Ernest Hemingway's 1926 novel "The Sun Also Rises." San Fermin is one of Spain's most famous fiestas and attracts thousands of foreign tourists every year.
Hillmann's wife Enid was at the hospital with her husband, Fiske-Harrison said.
Three other Spaniards who fell during the run were being treated in Pamplona hospitals for their injuries.
Several thousand people took part in the nationally televised 8 a.m. run.
Fifteen people have died from gorings since record-keeping began in 1924. Dozens of people are injured each year in the runs, most of them in falls.
The bulls are invariably killed in afternoon bullfights.