Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force. Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force. The reaction force is zero because the force of the bat on the ball is equal and opposite to the force of the ball on the bat. The reaction force is the force by the ball on the bat. The reaction force is the force of the bat on the ball. The reaction force is the force due to compression inside the ball: