If it is just the hind end, it is a spinal lesion, likely a stenosis or other malformation of the spine pinching the spinal cord. If it includes the front end, with just the hind end worse, it could be that,or a true Wobbler's or even an enzyme deficiency or other interesting thing. Either way, if drug free can be eaten, wouldn't want to grow it to full size because it will get worse and the animal could go down.
The reason I feel it's neurologic, is that you can see the crossing of the hind feet, and the stiff gait on the hind. The stumble on the front makes me think the front is involved as well. But hey, it's just what I saw.
Who's calf is this??