I was in fair shape, starting the build up about three months out when I got the most excruciating nerve pain in one ankle. Tried orthotics, PT, all kinds of things but literally didn't run more than a few steps at a time for 10 weeks. A few weeks before the marathon I tried a short run and it went OK, the weekend before I did 12 miles with some friends who were tapering. Decided what the hell, why not?
I had fun for the first 15 or so miles, cheering it up with crowds, walking through the aid stations, talking to people around me, running probably 30-40 seconds a mile slower than I was capable of if trained. Around 18 my quads were cramping so I stopped to stretch and lifting my foot up to my hand sent my hamstrings into cramps. So, yeah, jog-walked that last 8 with cramps front and back of legs. Still glad I didn't DNF or DNS.