What causes rand dead rings of grass?

[RLS 2010]

Anyone have any ideas what would cause random dead rings of grass like in the attached picture? This is in one of the lawns I mow, I haven't seen anything like it before. Also any idea what would cause a dead ring of grass about 15 out from an oak tree?

[Dave does lawns]

Beginning of fairy ring?

[R & R Yard Designs]

NRS That looks to be
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[grandview (2006)]

Fairy rings.

[RigglePLC]

Notice the more intense and sharper border on the opposite side of the ring. More diffuse on the near part of the circle. I suspect that someone was standing on the opposite side and tried to kill a weed in the center. Is that a clump of Bermuda in the center? Can you find a dead weed in the center. Maybe they were using a hollow cone nozzle.

Do you have big dogs in Leonardtown? Is there any sign of intensified green?

[RLS 2010]

Originally Posted by RigglePLC

Notice the more intense and sharper border on the opposite side of the ring. More diffuse on the near part of the circle. I suspect that someone was standing on the opposite side and tried to kill a weed in the center. Is that a clump of Bermuda in the center? Can you find a dead weed in the center. Maybe they were using a hollow cone nozzle.

Do you have big dogs in Leonardtown? Is there any sign of intensified green?

I'll have to check the center of the rings when I return Saturday. The customer did recently have a falling out with her Fert & Squirt company and was at one point spring dandelions as she saw them, so this is a very viable option. I'll try to get some better pictures too.