The american bison has a charge speed in the range of around 35 mph, weighing in at roughly 1400 - 2000 pounds. All of this calculates to over 13,000 Newtons of force.
A Lakota Sioux warrior's spear is only 57 inches, or about 4.75 feet.
Now adding that the Newtonian force required to break a human femur bone is around 4000 newtons, the most likely occurrence in this situation would be that whether or net the spear impaled the bison it would quickly snap or be torn from the young man's arms, and the bison would continue to quickly run him over.
So this would probably not be our friends most promising course of action. Sorry!
Now I was asked about my calculations. To calculate the amount of force in any situation, we use the equation; Force = Mass multiplied by acceleration.
For the mass variable in our equation we can estimate the american bison at 2000 pounds (probably the worst case scenario). we can convert that weight to just over 907 kg. The bison in question will have a speed of 35 mph, so where do we get our acceleration? In this instance we are concerned about the acceleration of the young man's spear, as well as himself. The young man is not moving relative to the earth but he will be quickly accelerated when the bison collides with his braced body. Thus our acceleration (the speed at which the bison will collide with the man and attempt to move him), at 35 mph is 15.6 m/s.
Sadly I'm a bit rusty when it comes to calculating force, but thanks to some comments I was advised on what needed to change.
So heres our calculation of acceleration: 15.6-0 divided by 0.05(the time in seconds, about halfway between an estimate given me) multiplied by 15.6 m/s^2
So this equation will actually give us a larger amount of force, because now our estimated acceleration is 20 m/s^2
So here's our equation now: Force = 907 kg * 20 --> Force = 18,140 Newtons
If our bison weighs in at a lower 1,400 pounds? Force = 725.7 kg * 20 --> Force = 14,514 Newtons
So when this best case scenario vs. worst case scenario are averaged out together it comes to about 16,300 Newtons! So after some recalculation and estimates, it seems the likely hood of surviving is even less likely, sorry again!