On November 21, 1963 Oswald learned the JFK motorcade would be passing by his window at work the next day. So he went home, brought his rifle to work the next morning and fired three shots at the President. One of which blew his brains out
That is all there is
Yeah, it's normal for a bullet to hit someone from the rear and force his head backwards.
Absolutely it is, for this reason:
The bullet exiting the skull released a lot of energy forward, pushing his head back. The film shows JFK's head first go forward, then back. Think about it, the bullet enters the skull through a small hole, then exits through a very large one, carrying a lot of tissue and blood with it. A bullet leaves the gun because the expanding pressure of the burning gun powder pushes on it and the breech. Since the bullet can move, out it goes. The same thing happened inside JFK's head. The bullet brought a lot of energy with it, and when the front of his skull blew apart, that's where the energy went, and Newton tells us that his head will go backwards.
Now if the bullet had remained in his head, it would have gone forward and stayed that way.