Developed tightness in my right calf at about 6.5 km, by 7.5 km I had to stop and try to stretch, stopping was the worse thing I could have done apparently, another .5 km later and I stopped again, I was bent over and taking baby steps hobbling, felt like a cramp, felt like a torn muscle, felt like pain, and lots of it.
I managed to keep some form so as not to hurt anything else on the way home. I must have been ripping along, because I know I was running slow the last 4k and still ran a pretty quick time for the course. Running down hill was quite easy, running uphill was painful.
I've been stretching all day, I even took a Ukrainian pain killer a very rare event for me. Right now, at 4:00 p.m. it hurts but I am limping less. Just need to see what happens, I don't think it is a tear, it is however, a serious cramp, drinking water and green tea.
Nothing lasts forever.