I just ran my first full Marathon on Sunday. I was feeling ok in beginning until 15th mile. I felt my left calf start cramping, After 5 miles, it became so sever that I had to stop to stretch it, then walk a few steps and run until it started cramping again. this happened during 20th to 24th mile. Around 24th mile, it became much lighter and I finally can pick up a little bit for the last 2 miles to finish. My right calf cramped a while in between 22nd and 23rd mile and disappeared without I realized it.
I think it's most like because my pace was about 10 sec. faster than my normal trainning pace. But just wanted to hear from other runners here becasue I found many advices here are very helpful.