The damaged skin is a physiological condition that can usually be blamed on rain. After a dry summer, a sudden downpour allows the plant to take up way more water than usual.
As a tomato takes up water, the fruit expands faster than its skin can stretch, causing the skin to split. What you get are growth cracks or “bursting” of the fruit.
But it’s not always rain that causes this—in hot weather, you might find yourself watering more often or more heavily as well, leading the fruits to swell and split.
The damage may appear as radial cracks (which extend from the stem down the sides of the fruit) or concentric cracks (which show up as a circular pattern at the top of the tomato, ringing the stem end).
If fruits are left on the vine, rot may set in at the cracks or the cracks may heal over with brown “scar” tissue.