I experienced a mild calf strain on the Sprint day of the 2008 North American Championships (there were two sprints that day). I suspect the cause was inadequate training followed by a particularly rigorous competition day. Descending stairs caused tightness and pain in my right calf. Running was pained.
1. Train adequately. Duh.
2. RICE was helpful with this injury, but ultimately lots of rest and adequate time were critical to recovery. I don't see how I could have taken less than 4 weeks to effectively recover (and even that was probably risking additional injury).