tight or pulled Medialis - that big muscle on top of the thigh

a month a go, i was doing the Welland Tri and about half way through the run, the left medialis just started to tightenup, almost like when you wring a wet towel.

at today's NYC Tri.. the second I hit the run, it started tighting again. It was super painful to the point where I had to stop every mile, walk for a bit, run again.

I wasnt toasted or anything, just in this weord pain.

Could this be the result of a cleat realignment I had done about a month ago ?

Would there be another reason the Vastus Medialis could be tightening up almost immediately ?

its too bad too, cuz i had a great swim, great bike, crap run..