It might be an optical illusion but it looks like the ground dips there and all the way toward the big ball. Does water accumulate in the area? If so then it might be a fungal disease problem.

I don't know where you live, but here in PA, so many lawns in my neighborhood are experiencing grubs. Can you pull back the sod easily and look for little white comma-shaped bugs that are eating the roots of your grass?

I suggest that you make a solution of water and dish detergent. pour about 2 qts over the yellow area. The grubs, if they are there , and look like a white Cheeto, will rise up to the surface. You may see just a few. This is not an infestation. More than about 1 per sq. ft. is an issue. Try Grub killers