Sounds like you may have cared for it too well. Sounds like the problem is what they call brown spot, a fungal condition. Fungal diseases spread under warm, dark, moist conditions. Never water lawns except during early morning light hours. At this point, when the lawn greens up in cooler weather and we have some rains, assess the lawn and plan to overseed with a blend of tall turf-type fescues. In the past, I have allowed bluegrass fescue lawns to aestivate (hibernate) in the summer by not watering at all and only fertilizing in late summer to early fall. This plus mowing high and often will encourage deep roots and thick turf.