Carl Akeley actually did kill an attacking leopard that way. Before the cat could disembowel him with its hind feet, Akeley rammed his forearm into the animal's mouth and pushed its head back until he broke its neck. He was ripped up badly but he did live; some survival manuals still recommend trying this if an animal of that size is trying to kill you.
Akeley was sent on an early expedition to shoot some gorillas and bring back their bodies for study, at a time when almost nothing was known about them. When he actually saw the apes and realized what they were like, he instead started working to establish a preserve for them in Rwanda.