For me, a great personal effort by a running back is the most entertaining thing to see in sports.
On Saturday, I watched one of the greatest runs that I have ever seen. This post is to preserve it so I can find it when I want to watch it again. Here and here are a couple my other favorites.
But, for my money, Barry Sanders put together the greatest number of physics-defying runs ever. If you watch this video, notice how many guys that are trying to tackle him just completely whiff.