Bounce of an oval shaped football

Abstract The bounce of an oval shaped football may appear to be erratic but it can be described by simple laws of physics. Projected at an oblique angle without spin or with backspin, a football usually bounces backward if the top end points backward on impact. Projected with topspin, a football usually bounces forward. A football incident with topspin will sometimes bounce to a much larger height than usual, and other times it will roll for a short distance before it bounces. These effects were examined by filming the bounce with a video camera, and explanations are provided in terms of the normal reaction and horizontal friction forces acting on the ball. A surprising feature is the fact that the friction force can reverse direction 3 or 4 times while the ball remains in contact with the surface.