The momentum of a player changes when his speed changes and when his direction of travel changes. Large forces are involved in quick stops and fast turns. The same maneuvers require larger forces when executed by more massive players. A player must be able to take what he dishes out. When he applies a force to an opponent, he is acted on by a force of equal magnitude.
Good footing is important.
Forces exerted by the ground play an important role in all maneuvers. Leverage is important. If the force has a large lever arm the opponent can be spun around. In the coming weeks we will explore the physics of the forces on the field.