Oblique Collisions of Baseballs and Softballs with a Bat
  Experiments are done by colliding a swinging bat with a stationary baseball or softball. Each collision was recorded with high-speed cameras, from which the post-impact speed, launch angle, and spin of the ball could be determined. Initial bat speeds were in the range 63-88 mph, producing launch angles in the range 0$^\circ$-30$^\circ$ and spins in the range 0-3500 rpm. The results are analyzed in the context of a ball-bat collision model and the parameters of that model are determined. For both baseballs and softballs, the data are consistent with a mechanism whereby the ball grips the surface of the bat, stretching the ball in the transverse direction and resulting in a spin that was up to 40$\%$ greater than would be obtained by rolling contact of rigid bodies. Using a lumped parameter contact model, baseballs are shown to be less compliant tangentially than softballs. Implications of our results for batted balls in game situations are presented. 
Jeffrey R. Kensrud, Alan M. Nathan, Lloyd V. Smith
physics.pop-ph