A rubber ball of mass m and radius R is filled with air. The excess pressure inside the ball is $\Delta P.$ However, mass of the air in the ball is negligible. The ball surface is flexible but non-stretchable. When you push its surface at a point with your finger, the ball’s surface in contact with your finger gets flattened as a circle of area A. In this position, the ball exerts a force $\Delta PA$ on your finger. We will assume that when A is small, the excess pressure remains unchanged. Such a ball strikes a vertical wall when moving horizontally and rebounds with its speed unchanged. The ball remained in contact with the wall for a time interval $\Delta t.$ Assume the deformation in the ball to remain small.

Contact area between the finger and the surface of the ball is A. Force between them is $\Delta PA.$