Bison converge in Yellowstone during mating season, and a visitor's film shows one of the beasts headbutting an automobile.
Because of a herd of bison that had blocked a route in the Hudson Valley section of the park, the car and many others were stuck there.
William Ogonowski, who was riding in the car just behind the one the bison slammed, filmed the incident.
"Nooo, they're heading right towards us.
They're brawling in plain view of the onlookers "Ogonowski is heard stating in the footage just before the attack takes place.
Bison are making their way to Yellowstone's Lamar and Hayden basins for what the National Park Service (NPS) says is rutting season.