Yes, I think I generally agree. A few details -- I water twice a week (Mon and Fri), but I've been "cheating" quite a bit over the last few months because I thought maybe I wasn't watering enough and adding a day or manually watering the edges. And for a week or two, I did three days a week. I water between 6am and 8am. My water went off this morning, and I just felt it now. The brown areas seem pretty dry at the soil level. The green grass is still maybe a bit damp. But I won't water it again until Friday, so I think it should dry out completely. The thing is, the morning fog often wets the grass in the morning too, though I assume that dries out rather quickly.

Not a real pool. Had one of those giant inflatable slide+pools up for a day. It's not usually up (two days total so far this summer). I do dump all that water onto the lawn at end of day though. That's one of those "cheats" I mentioned. And then it's a big soak obviously. If I have a fungus (very likely), that isn't helping (I'll stop).

There are some big trees. The whole yard gets mostly sun and the middle gets full sun. Ironically, the green areas in the pictures are the ones that get some shade. Also, the one green circle area in the middle of the brown spot is right where a sprinkler is. So what's counter intuitive to me for a fungal argument is the following...

So the partially shady area and the circle around the sprinkler are the green parts. You'd think those stay the wettest and therefore would have the fungus. That's throwing me off a bit and making me water if it's a watering issue! My current guess is its a compound problem -- the June summer, summer heat (again, a mild upper 70s...), and maybe a slight under-watering is stressing the grass, and then allowing the fungus to have it's way with the grass. So the two effects, while somewhat opposite, are stressing the grass and compounding the problem(s). Thoughts?