These issues are very difficult to pinpoint because many times the source of what you are experiencing is not the cause, but could be anywhere along the kinetic chain. For example, my tight calf was not caused directly from my calf muscle but was a by-product of poor glute strength and tight hip flexors which in turn forced my quads and calves to carry too much of my running which overtime caused my calf issue.
The numbness, however, suggest it could be nerve related. It could be a tight piriformis which is a small muscle that lays over the sciatic nerve which runs down the leg. HOWEVER, only your doc or sports chiro can tell you for sure. This may be a good time to write down whatever you were doing (just finished hill work, speed work, stopped to pick up something, etc) and make a notation in your running journal so that if this happens again you will be able to help your doc help you.