What kind of grass is that and do you have a female dog?

Not sure the type of grass...and no female dog but house on next to a backlane so it is very possible that dogs have peed on the lawn.

I would second the notion that it is probably a dog issue.

I've also had a past similar issue when i had a riding lawn mower that exhausted onto the grass and if you stopped for an extended period of time would kill a perfect circle like this.
I would not say that it would be a grub spot either (a bit TOO dead).

Did you fuel the mower when you mowed?

If so is that where the spot occurred?

Did you wash paint brushes, or something similar