The noted naturalist, taxidermist and wildlife sculptor Carl Akeley killed a leopard that jumped him by forcing his fist down its throat and then crushing its ribcage with his knees. The leopard was not a huge one, only about 80 pounds according to some accounts, but Akeley wasn't in very good shape either, having just recovered from a bad bout of malaria.
American frontiersman, African adventurer and professional hunter "Bwana" Charles Cottar was once jumped simultaneously by two leopards. Cottar, a large, powerful man, grabbed each of them by the neck and killed them by bashing their heads together repeatedly. I suspect the leopards may have been subadults, but even so, it would be a very impressive feat. Cottar was eventually killed by a charging rhino.