The annual event, made famous in Ernest Hemingway's writings, involves a herd of bulls, used for bullfighting, charging up a 900-yard street to the bullfighting arena. Participants dressed in traditional white costumes run ahead, and look for a way out of their path in a process which typically takes about four minutes.
Ryan, 50, recently underwent gastric-band surgery, and looked good while running with the bulls, said participant Matt Stevenson of Austin, Texas.
"Yes, the Jets coach. Lost a bunch of weight and was with his son. So weird," Stevenson in a Twitter comment.
Before the running, Ryan was in a jovial mood, in a shirt with a cartoon bull and the phrase "Bad Toro," as he posed for pictures with friends and Jets fans, the New York Post reported Tuesday.