Very unusual pattern for a fungus.
Red thread fungus is a possibility. Pinkish color. Some types of perennial rye are sensitive to red thread.
Take a soil sample.
Is there a mole in a crazy mood?
Did someone spot spray something in an unusual pattern?
Is there a dead weed in the center of each spot or line? I think I will look again.
Did you dig down and check for grubs?
Gasoline leak from mower or trimmer?
Hydraulic leak from equipment?
Was something left on this spot and removed before you got there?
I saw a spot like this years ago.
Workmen cleaned their paint brushes and made a spot.
Smell the spot: oil, gas, solvent.
Also, sometimes homeowners spray some weeds--with Roundup.
Think about salt or deicer. Compare pictures of snowmold.
There appears to be a "frog eye" pattern developing...brownish ring and green center. Possibly fusarium, or as it is called now, summer patch I believe. Just a guess on my end. But I agree, very strange pattern
Is this lawn in South Africa, Bolivia or cool season grass in the United States? Please narrow down your grass type, location and weather patterns the last couple weeks. I have seen just a bit of this in fine fescue this year that was very long under wet conditions. Potentially Red Thread or maybe Michrodocium.
Circular patterns tend to be organic--probably fungus.
However, square patterns tend to have human or a machine cause.
Were any fireworks thrown here?
Any sign of mower exhaust from a mower idling?
Did customer try some new kind of organic weed killer he learned of on the internet? Vinegar? With salt?
I am leaning towards hydraulic oil leak. Is this where the Scag turned around?
I remember when a customer called about mysterious brown spots near the back fence of his yard.
There was a Burger King just over the fence. A big dumpster was just over the fence. Then it became clear.
The big trash truck hydraulic dumped the trash dumpster. And a hydraulic hose had a leak that squirted out hot hydraulic oil, this at high pressure. Reached a distance of 10 feet.
I think this spring being cooler with less moisture is triggering turf to go in and out of dormancy. People can’t understand why a lawn isn’t thick and green because it’s May. We have patchy lawns and lawns under drought stress. Tire tracks from mowing through dry spots and we just reached may. We have been showing soil temperature maps to customers to help them understand.