Aerodynamic forces on a spinning golf disc. By DrD, http://www3.telus.net/discgolf/disc.png Found at PDGA DISCussion, http://discussion.pdga.com/msgbo

There is a gyroscopic effect that occurs that causes any disc to bank or fade in the opposite direction of rotation. If a gyro (disc) has rotational input applied on a horizontal axis, the gyro (disc) will be rotated on the perpendicular horizontal axis. Deflection occurs 90 degrees from the rotational direction (spin) and the rotational input (angle). The rotational input is created by the disc following the arc that all projectiles follow in sub-orbital flight. Of course a disc has lift, so it is a bit more complex, but all of the thrust needed for lift occurs before the disc is released. After that, drag has an immediate and constant affect on the speed of the disc and the disc only has enough lift to overcome gravity at higher speeds (every disc has a different speed at which it generates enough lift to overcome gravity). Rotation also slows due to drag, but it is only reduced. At the end of a disc's flight, it is much less "stable" than it is at the beginning of it's flight due to three factors. 1-the slowing rotation of the gyro 2-lift is greatly reduced because of it's slow speed 3-the path of the disc at the end of the flight arc creating rotational input along a horizontal axis.

http://en.wikipedia.org/wiki/Gyroscope