The bison charged the crowd, goring 59-year-old Kim Hancock of Santa Rosa, California.
At one point, people were closer than 15 feet to the bull, officials said.
The crowd came within about 10 yards of the bison while walking along the boardwalk. It left the area immediately following the incident.
Ranger responded and treated Hancock for a hip injury.
Millions of American and global visitors crowd the park each year to view wildlife like bison and natural wonders like the Old Faithful geyser.
Park officials said she was in good condition.
Earlier in the week, two women were injured by elk, one on Sunday and another on Tuesday. Because of the severity of her injuries she was flown to an Idaho trauma center.
Donald Trump "probably" on board with bipartisan pot bill
For his part, Sessions told Colorado Public Radio that he was excluded from conversations between Trump and Gardner. A new bill introduced in Congress on Thursday could change that - all without federally legalizing marijuana .
The retiring head of Yellowstone National Parks accused the Trump administration of forcing him out early over squabbling with the Interior Department.
If he accepts the new job, Wenk said he would need to make a commitment of at least three to five years "to honor that region, those parks and those employees".
Safety tips from Yellowstone park officials can be found here. Officials caution visitors that animals in Yellowstone are wild and unpredictable, even when they appear to be calm.
The park service recommend people stay at least 25 yards away from animals like bison and elk and at least 100 yards for bears and wolves.
"I'm feeling like I devoted 43 years of my life, I think I have a record of achievement with the National Park Service that at the end of the day doesn't matter and that I'm no longer wanted at Yellowstone National Park", he said in an interview with Yellowstone Public Radio.
"If you can't maintain these distances, turn around and find an alternate route", the park advised.