Your non-throwing arm, my friend, might seem like it's just hanging there, but its position is actually really important for your overall balance and keeping your body from rotating unnecessarily during the throw. If it's swinging wildly, it can throw you off balance and pull your dart off line.
Many players find it helpful to keep their non-throwing arm relatively still and close to their body, either resting gently at their side or extended slightly for counter-balance. Avoid letting it swing around or use it to brace too much against the oche. Its main job is to stay relaxed and help you maintain your balance throughout the entire throwing motion. Some even use it as a subtle pointer, but its balance role is primary. A disciplined, quiet non-throwing arm ensures your throwing arm can work independently and accurately.
