The composition of the band typically is metal, leather or synthetic material of some type, such as plastic. You should look for a band that fits your wrist correctly, no matter what the style of the sports watch is or what the composition is. Any watch that is too lose will tend to catch on objects while the wearer is active. A watch band that is too snug will never be comfortable to wear and will tend to rub or chafe the skin of an active wearer.
The watch crystal is generally not an option on a sports watch or any other. You will find the harder the substance the better quality the crystal. Synthetic sapphire is the typical choice, as they are next to diamonds in the hardness scale. Less expensive watches will typically use mineral glass or even plastic. Mineral glass is coated so as to make it more resistant to scratching.