I've been training for a half marathon and the past few days the big toe ok my left foot is shooting pain up past my ankle, what is causing ths?

See an orthopod: Or a podiatrist asap as that is not normal and if you keep training on it without knowing what is going on , you may not be able to run your race, as a veteran of 7 marathons and 15 half marathons, the #1 reason people can't run the race is a pre race training injury so see a doc today.

Could be : Tendonitits of the extensor tendon to the big toe, or could be a radiculopathy coming from the lower back. Those would be my first thoughts. Make sure your sneakers are proper size, make sure you stretch, consider arch supports if you aren't already using them. If pain persists visit a doctor.

Neuritis/tendonitis: Shootung pain sound like neuritis. A tendon that inserts at big toe and originates above ankle could also be inflammed.

Tendon or nerve: Nerves pain is typically when you move the toe , where nerve pain may be intermittent and hurt worse when doing nothing. Try Motrin and take a couple of days off running( try swimming) . If it continues see a podiatrist.