In hockey there are lot of continuous collisions. With each collision momentum between each player is changed. For example, when player A is skating across the rink and player B comes in contact with player A, player A's speed is changed, thus altering his momentum. Depending on the force between each of the hockey players, the course of on of them would be completely altered. On the other hand, the player with the greatest force would not change his direction, instead his speed would be the only thing that changed for him.