Was the reseeded area soil that was dug up for some type of construction or something? If so, was the topsoil and subsoil mixed?

A *good* soil test is a great way to find out why the grass isn't thriving in the soil. Logan Labs has the most complete soil test at a reasonable price. Many "cheap" co-op tests have so little info that they are worthless at diagnosing a problem.

How often and for how long are you watering? It could be the short little grass roots rotted from being saturated all the time. New seed should be watered 3x per day until it sprouts. Then back off steadily until you are watering a full inch, all at one time, every 10 to 14 days. When the temps get into the 90s every day, then move to watering every 7 days. Measure how long it takes your sprinkler to water an inch by placing cat food or tuna cans out in the yard.

Also you will be much, MUCH happier with an oscillator type sprinkler than the RainBird type. Oscillators apply a very even coverage. RainBirds shoot water out which lands at the circumference of the circle. When you get an oscillator, get the turbine type (about $20). The mechanical linkage kind are harder to get adjusted right and seem to stop working in a few months.

At the end of next fall be sure to Winterize right when the grass stops growing. Then next spring don't fertilize with anything until late April or May AFTER the normal flush of spring growth is over. If that means you have to mute the Scott's commercials on weekends, then so be it. They have already sold you unnecessary stuff.

If you want to kill weeds next spring, spot spray with the appropriate weed killer.