Rotational Motion

The angular acceleration is defined as the rate of change of the angular velocity.
The angular velocity changes when the rotation rate is increasing or decreasing and when the axis of rotation changes direction.
A larger torque produces a larger angular acceleration. You can get a larger torque by applying a larger force, or by using a longer lever arm.

torque = lever arm ´ force,

If the interaction force is applied near the center of mass of of the player, it produces no torque, and therefore no angular acceleration. Immediately after the collision the player has no angular velocity about his center of mass.

If the interaction force is applied away from the center of mass and produces a torque and therefore angular acceleration the player emerges from the collision with angular velocity and will have a hard time staying upright.

Coaches often advise linemen to stay low. With their center of mass closer to the ground, an opposing player has to tackle them near their CM. The lineman is then less likely to rotate, fall over, and be moved out of the way. This technique is critical for a defensive lineman in defending his own goal in the "red" zone, the last 10 yards before the goal line.

After the collision the player is only acted on by gravity and the normal and frictional force due to his interaction with the ground, unless he immediately collides with one ore more other players. These forces can also produce torques about various points in his body. The player may be able to shift his center of mass in such a way as to minimize these torques. A player at rest with a wide foot stance is better able to do this that a player running at full speed with only one foot at a time contacting the ground.