The spot with your hand looks like it could be grubs. Although this has been one of the quietest years for grubs/japanese bettles I have ever seen. Dig back a piece of lawn and see if there is any. Soulution is Dylox (commercial grade pesticide) or if the home owner is doing it use Grub-X but make sure its the one with the "Bayer" symbol on it as it uses Dylox as well and either way it will kill the grubs (and moles) in 24 hours.
If grubs are not the case I would say over watering for a shaded area. It looks like the roots are drowning. Cut back on the watering.
It doesnt look like excess nitrogen to me.
lol and Scotts "dog pee" theory would cause the lawn areas to become acidic and the solution would be lime to bring the ph back up.
Let us know if you find grubs Tom.