One thing that I’ve seen repeatedly over the years is that when a person gets a sudden Charlie horse, or violent calf cramp in his/her calf, the first remedy they try to do is stretch. This is the exact opposite thing of what you need to do, in fact, stretching can cause the muscle fibers to tear and is the reason you may limp for days after a cramp.
Think of what would happen if you took a 12″ line and tied it into multiple knots, until the line was only 10″ long. Then you tried to stretch it back to 12″ again without untying the knots. The knots become tighter and the fibers outside of the knots will be overstretched – perhaps to the point of tearing. The same thing happens to your muscle.