Wyoming, G.T.N.P., Blacktail Butte. On 28 August William Clark (19), was belaying Douglas Boggie (27), both relatively inexperienced, while Boggie tried a difficult section of the practice cliff. According to Boggie, he was about 20 feet above the scree slope and about 10 feet above a moderate sized ledge, when he fell. He immediately felt the rope slip as he landed on the ledge. Clark slipped from his belay stance and fell about 50 feet onto a steeply pitched scree slope. Clark was knocked into a semi-conscious state and remained so while he received first aid during the rescue operation. He suffered a broken right upper arm, fractured skull, multiple lacerations and bruises, a ruptured diaphragm, collapsed lung, and ruptured spleen. He was not wearing a hard hat.
Source: Ted Wilson, Park Banger, G.T.N.P.
Analysis: Clark was belaying without an anchor. Since this is such a fundamental aspect of belaying, it can only be attributed to his inexperience.