Originally Posted by SystemicAnomaly
^ You are incorrect about corkscrew spin in tennis. Physicist, Rod Cross, had thought very much about the physics of tennis and disagrees with you. One does not hit the side of the ball to impart corkscrew spin. However, the contact is offset to impart this type of spin.
This type of spin can also be imparted to underhand shots with very dramatic effects.
Corkscrew spin on a twist serve is negligible. Cross mentions spiralspin as the type of spin put on a football. He suggests that it is possible for tennis. However, he didn't find much spiral spin on twist serves.
As for underhand shots (or to a smaller extent for a twist serve with initial upward trajectory), the spiralspin is initially zero, but increases as gravity changes the path of the ball. The spin immediately after contact with the strings is not sprialspin - a tennis racquet is not designed to impart spiralspin.