The simulation of collisions becomes trickier when tangential compliance cannot be ignored. For example, a ping-pong ball (very high tangential stiffness) rotating around an axis perpendicular to the motion falls straight on a table and bounces back up; the rotational velocity decreases, but it does not change sign. Whereas a superball (low tangential stiffness) will change the direction of the rotational velocity. I did my PhD on this, back in 2000, but haven't kept up with the field.
If anyone is interested in a way to take tangential compliance into account my thesis may be of interest: