Paul Jocelyn, 37, of Albertville, Minnesota received a puncture wound in his inner right thigh as well as scrapes and bruises after he approached the bull bison on Saturday near the Old Faithful Geyser.

Park officials are constantly warning visitors to stay far away from bison, who appear very docile, but in fact the animals that weigh up to a tonne are ornery and can sprint up to 30 miles (48 km) an hour. It is against the law to approach within 25 yards (25 metres) of wildlife at the park.

The bison was grazing when a group of visitors approached it within a dangerous 10 to 15 feet (3 to 5 metres). Jocelyn walked around the front of the bison to see if it would raise its head for a better picture.

The bison then chased the man into the trees and threw him into the air. The bison stared at the visitors for several minutes before walking away and resuming his grazing, the park said.