Can you get closer pics & tell us what city you're in?

I will try to get a closer picture tonight. It will be dark but I should be able to light it up ok. I live in Valley View TX 76272 which is just North of Denton TX.

WHat is your watering schedule for the past month or so?

Here are 2 more pictures a little closer up. I put one as a good area on bottom and one as a bad area on top so you can compare, the grass is just starting to change and go dormant but thats not really the issue, it appears to be this black stuff is the issue. As far as watering schedule, it has cooled off so I am watering one heavy day a week probably 1/2 or so about 5:30am just before the sun comes up. I am also watering 2 other days for 5 minutes about 10am. That is probably a tenth of an inch or less. I cut the water off when we have rain. It is only spots that look bad, most of the yard looks great but this stuff is in patches in front and back, in shade and sun.

I'm considerably south of you and a touch warmer. Based on rainfall I've only watered once in the past 2 months. I think you're watering far too frequently. If you go to monthly watering now (or less depending on rain) it should recover by April and look normal as it comes out. In April start with monthly watering and work your way up to more frequent watering.

As to why this spot and not others, perhaps there is better drainage in the rest of the yard. Or it could be there is more sprinkler overlap in this area.

Thank you, I was wondering about that. It might not help that there is a lot of thatch in that area too, it might be holding the water. I have very sandy soil so my water drains really well normally. I appreciate your reply and will cut the watering out for now.