This black walnut tree was planted (transplanted) to its current site 5 years ago. Most years since it has had some pretty gnarly looking bark. Often the lead shoot dies back and it sends up new growth from near ground level - often very vigorous growth (one year it grew 3-5 6' shoots in a couple months).
Now it looks worse than ever. A lot of the bark is completely gone.
The bark has been stripped by deer. Try cutting it back to its base and putting a four foot "coil" of chicken wire around it until it is several years old. The deer don't seem to rub against more mature trees because they don't flex as much.
Sounds like that tree is a popular one among the buck crowd. We have hundreds of black walnut of around that age but the bucks leave them alone. Here, their preference is for the young hybrid poplar and black locust saplings. Luckily, both of those coppice well and always spring back with vigor.
Anything that gets in the way of their antlers will discourage them. I've used black plastic drainage tile, split lengthwise as a protector. Leaving lower branches on or letting weeds grow tall around the tree also discourages them. I've had this idea about hanging a piece of rope on the trees that size to see if that would discourage it. That is on my to do list for this fall, selectively, to see if it makes a difference.
20 acres, previously farmed with tree lines, 36' of elevation change over 1,300 feet of south facing slope, 7,000+ trees planted so far in previously tilled acres at a density of ~500 per acre.