I was invited to look at this lawn. After discussion, it appears the lawn has several issues. It was over-seeded last fall. Some of the turf is still young. It has been fertilized perhaps too much in places. The leaves and stems had lesions.
Cure - mow tall and water as needed. No fertilizer until fall. If the weather stays cool, the turf will improve. If it come hot, the turf will decline and need attention come fall.