The short video illustrates the astonishing speed of which these animals are capable and, by extension, the inadvisability of attempting to run from bears; unless you're Usain Bolt, they will outrun you. And we're guessing they could probably outrun Usain Bolt, too.
The bears in Katmai Preserve are well known for their comfort with humans, but this big male is not above being irritated at human proximity. For the folks who got to see the bear enter, well, beast mode, it was a once in a lifetime event the won't soon forget. Check out the lady at the end of the footage, who is either spectacularly calm in the face of that much ill-intentioned furry flesh flying at her, or is in shock.
See the frankly ridiculously scary video below.