[rwest]

After thinking about it from a physics standpoint, I believe I know what is happening. Still not 100% sure because I can't slow it down frame by frame, but the physics works.

Both players are of a similar height and weight so there mass is going to be similar. They are both moving but in different directions. The offensive player is moving faster than the defender. So the offensive player has greater force. However, I don't believe the force from the hip contact is enough to displace the player. Remember, we have to take into account the force the defender is exerting. The force the offensive player is generating has to be sufficiently greater than the defenders to account for the displacement. I don't believe it is. It is however enough to cause him to be off balance. The elbow then causes him to be displaced like he was. That is why it appears to me that the defender gains momentum when contact occurs with the elbow. The hip caused the player to be off balance but it was the elbow the sent the player to the floor.