In 1978 my family was in YNP and the and a ranger told us that the week before a woman was killed by a buffalo. The buffalo was laying down and and the woman came up from behind and kicked it so she could could get a close picture of a buffalo standing up. The buffalo did get up but she did did not get a picture.
In 2002 my wife and I were back to YNP in the fall. All the bathrooms had signs which stated that the buffalo caused far more injuries than any other animal in the park. A fair number of people seem to not have any common sense.