Answer: It's likely that one or more diseases attacked your tomatoes. It's difficult to diagnose exactly what disease is causing the leaf symptoms, and it's not all that critical to make a positive ID; the controls for most diseases are similar.
It sounds as though the tomatoes themselves suffered from sunscald. As the foliage died back the fruits were subjected to intense sunlight, which can cause discolored or hardened areas on the fruit. On healthy plants, the tomatoes are somewhat shaded by the foliage.
The first step is to choose at least some disease-resistant varieties. Then, be sure to provide a thick layer of mulch underneath plants, since many tomato diseases are soil-borne and spread when rain splashes soil up onto the leaves. Since your plants are trellised, this should help. Some people find they can slow down the spread of disease by diligently picking off affected leaves and removing them from the garden. There are some new organic, soap-based fungicides that are showing promise, and sprays made from neem oil also have shown some fungicidal properties.
Q&A Library Searching Tips