Since you are nearsighted, you can wear prescription sports eyeglasses. The prescription sports eyeglasses are specially designed for sports. They are impact resistant so they are very safe for playing sports and they also can provide clear vision. I think it's a good idea to wear prescription sports eyeglasses when playing sports.
A good way is to wear a pair of goggles over your glasses. The goggles should fit snugly over your glasses and they must have anti-fog coating on its lenses. If you often play sports outside, the goggles should also provide UV protection.
It is unavoidable to knock down your glasses when playing sports if you are not careful enough. The best way to protect your eyeglasses from being destroyed is to cover them with protective devices such as safety goggles or protective helmet.