This pitch of a thrown gyroball really explains well how the spin is imparted on the ball. I have seen gyroballs thrown over 90 mph. The movement is usually straight but it drops more than normal because it lacks backspin.
This video also shows why and how the gyro spin is created by pronation of the arm before release.
http://www.youtube.com/watch?v=XEzHVtEHYNk