So two schools of thoughts.
1. It's new muscle use.
2. It's over use muscle.
I've never been so depleted of nutrients that my calves cramped. However the two times that I did get cramps it was from new muscle use. I changed cleat position slightly, that night woke to cramp in both calves. Not sure if I changed back or left it and acclimated to it. Possibly the latter. The second time, was in a duathlon. I wasn't able to run train for 2 weeks due to an injury. So I ran the hilly 10k in 36-7 minutes. Then hopped on my bike and rode a couple of miles til I got a cramp from hell in my calf, when it finally subsided, it's twin brother hit me on the other leg. Still finished strong and much less sore than I anticipated.