I guess you gotta be a pretty cool customer to pull it off, since you'll only get one chance to make it good, and if Mr. Griz or Simba swats it aside, you're lunch.
Seems like the planting of the spear technique might work with a big cat. A big cat will jump right into you and ignore the spear. A bear, though, likes to stand up and swat; some kind of Ultimate Boxing. Odds are not good mano a mano. The grizzly is soooo big that if you can get behind his shoulders he might not be able to reach you. It would be historical if you managed that one.