When I was training a guy in pre-season college football, I had a University track coach tell me that the reason you get them is because your calf muscle is basically to strong for the rest of your muscles in your lower leg (in front of your calf) He told me to sit on the floor with your legs straightened in front of you, like you are trying to stretch your hamstrings, then take a belt and hold each end in your hands with it strung around the part just below your toes. what you want to do is pull on the belt for a couple minutes at a time and stretch your calf muscles. he said that some people actually put weights one the tops of their toes and try to build up the front part of their legs by lifting the weight up and down with the tops of your feet---Kinda a reverse calf raise.
hope this helps