On 1 May, a woman from Idaho was slightly injured as she walked on a trail in the park.
Hancock was treated for a hip injury and taken by ambulance to a hospital in Montana.
According to a press release from the park, Kim Hancock of California, 59 years old, was gored by a bull bison at Fountain Paint Pot in the Lower Geyser Basin.
When the bison crossed the boardwalk, it became agitated and charged at the crowd and gored Hancock.
Safety tips from Yellowstone park officials can be found here.
Park officials said that, at one point, people were less than 15 feet from the bison.
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The incident comes on the heels of two elk attacks earlier this month, Yellowstone officials previously said. There was also one previous year and five in 2015.
Two women were injured by a female elk with her calf outside a Yellowstone hotel in separate incidents on Sunday and Tuesday.
Hancock is the second person to be attacked by a bison this year, and the third hurt by wildlife in less than a week.
Yellowstone warned that animals in the park are "wild and unpredictable, no matter how calm they appear to be". "When an animal is near a trail, boardwalk, parking lot, or in a developed area, give it space".
Yellowstone requires that visitors stay at least 25 yards away from bison and elk and 100 yards away from bears and wolves.
"If you can't maintain these distances, turn around and find an alternate route", the park advised.