Being new to lawn care you are probably watering too frequently thinking that the grass is dry. Another possibility is insects. Grubs from Japanese beetles or June bugs can get into the soil and eat the roots. You can check for grubs by digging up one square foot of grass. If you see fewer than a dozen grubs, then it was not grub damage. If you see an uncountable mass of grubs, then that was the problem. Spraying now is more satisfying than it is helpful as the grubs have stopped feeding. Another possibility is disease from watering too frequently. Can you take a picture, preferably on a cloudy day with no flash? Get down about 3 inches away at a spot where the grass is on the fringe of green and brown.

Do you know what kind of grass you have? Could it be zoysia?

Here's more on watering.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

Now is the best time of year to reseed if you want to have a nice lawn for next year. Need to know what kind of grass you have before doing that.