Yes, that is exactly what happened to me about a month ago--sudden onset of pain during 5K race (done at a PR pace!), following some tightness that I had experienced during long runs building up to and including my IM. At first the throbbing pain was so bad it would wake me up at night--glut, down through lateral hamstring, through calf and around top of foot. My self diagnosis is piriformis syndrome (google it and search the main forum). As I understand it, when the piriformis is inflamed it can put pressure on the sciatic nerve.

About a month later, with lots of stretching and rolling, it's much better. I still have to be careful. I find that if I tense up or try to run fast it aggravates it, as do hill repeats. Here is a good site to start with:
http://www.athletestreatingathletes.com/body-resource-map/hip-posteriorback-of/

It literally is a PITA.

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No coasting in running and no crying in baseball