There are a few reasons why your protein balls might be dry or crumbly. One possibility is that you didn't add enough moisture to the mixture. Be sure to use a nut butter that is smooth and runny, and consider adding a bit of almond milk or water to help bind the mixture together. Another possibility is that you used a protein powder that is too dry or that absorbed too much moisture from the other ingredients. In this case, you might need to adjust the amount of protein powder you use or add a bit more moisture to the mixture.