Lawn, diseased or ?
Let me start by asking you a few questions about your lawn. What is the exposure? Which direction does it face? It looks like it might be on a hill. Is that correct? It looks extremely dry and given our fairly generous moisture this winter, it makes me wonder if run-off is an issue. The damage looks like dog pee damage. Dog pee is straight nitrogen which kills the grass in the immediate area of urination, but acts like a fertilizer on the perimeter, hence the color. Do you or did the previous owner have a dog? Can stray dogs use this as a potty spot? The damage in general looks like neglect and lack of water. So without any more information I would have the lawn aerated and overseed it with a grass of your choice. Make sure you water or use irrigation to give the lawn about an inch of water a week. If the lawn is on a hill, make sure you water more often but not as long since you don't want to incur run-off, which is common on clay soil. Clay takes longer to absorb moisture. Here is the link to a fact sheet that outlines how to renovate your lawn:
Please don't hesitate to contact us with more questions.