Have you sprayed or spread any kind of insecticide or weedkiller around it? Burned it watering in the hot sun? Isn't it awful late for cabbage in zone 8?

Check roots for root maggot

I'm in zone 7, didn't think it was too late, never grown cabbage, these were given to me by a friend who purchased too many plants. I have not sprayed anything or watered for that matter (we have had lots of rain).

I'll check the roots, this appears to have happened to 3 or 4 plants.

Thanks for your help!

Cabbage will grow in the summer in the Shenandoah Valley, Root maggots were a big problem for me in the New River Valley, so that could be your problem. There are also root rots that affect cabbages.
ruthieg__tx ; USDA zones are pretty meaningless for vegetables. Remember that parts of Canada are zone 8. It only refers to winter temps for perennials not summer heat.