What is Stability? It is a description of a disc’s general flight path, it's Turn and Fade.
---Understable means a flight that turns right (for a RHBH thrower).
---Stable is a flight that is basically straight, does not turn.
---Overstable refers to a flight that turns left (RHBH thrower).
Understable discs are the most speed sensitive. Thrown at a higher speed, they are likely to be more understable (go right), at a lower speed they are likely to be more stable (straight) or slightly overstable (go left). That is why understable discs are the best for beginners as they tend to throw discs at lower speeds.
Pitch - Pitch refers to the 'nose up' angle at which a disc is released. Drivers are more pitch sensitive than Multi-purpose or Putt & Approach discs. Drivers thrown 'nose up', with an upward pitch, will appear to fly more stable (straight) to overstable (left) than they are actually rated. Beginning disc golfers tend to throw nose up shots.
Click here for info on DX, Pro, Champion, and Star Plastics and their affect on Fight Characteristics.