Unstable

When you attack while unstable.
Difficulty modifier changes according to how unstable you are.
For example:

• Ranged attack while riding: +4.
• Hand-to-hand combat while riding: +2.
• Swordfighting on a precarious hanging bridge: +1.
• Dagger duel on a narrow plank above a pit filled with poisonous snakes: +2.
• Unarmed combat on a log floating in a rapid river: +5.

The GM has the final call, use this as reference.

If you try to reload a projectile weapon while riding, you need to roll Agility & Riding, with a +2 penalty because of being unstable.