I don't know which part of the course you are trying to replicate.
Deformation is the distance of the node from its initial position to its current position. Wait a second and the deformation will be measured in meters!
During the impact of the ball and the bat, you can measure the deformation of the ball relative to itself by plotting Strain instead of Deformation. The strain of the ball is zero as it flys toward the bat, though the deformation of the ball is increasing.