"When it crossed the boardwalk, the bison became agitated and charged the crowd, goring Hancock", park officials said, adding that the animal left the vicinity right after.
Park officials say some in the crowd came within 15 feet (4.6 meters) of the bison when the safe distance is at least 75 feet (23 meters). She was transported by paramedic ambulance to the Big Sky Medical Center in Big Sky, in good condition.More news: President could face questioning by next year in defamation suit
The two women were among four people injured by various types of wildlife in the park in just over a month.
Rangers recommend park visitors stay at least 25 yards away from animals, and at least 100 yards away from bears and wolves.
According to the National Parks Service, bison have lived in Yellowstone since prehistoric times, but went almost extinct in the USA after excessive hunting in the 1800s. An elk also kicked a different woman's head Sunday, but the park service said it was unknown if the same elk were responsible.More news: Thiem ends Cecchinato fairytale to reach French Open final
The incident on Wednesday is the second time a park-goer has been attacked by a bison this year.
Park officials instructed visitors to give animals space, even near trails, boardwalks, parking lots and other developed areas. On 1 May, a woman from Idaho was slightly injured as she walked on a trail in the park. "If you can't maintain these distances, turn around and find an alternate route".More news: CDC report reveals more than 45,000 Americans took their own lives in 2016