Maybe it is an earthworm...just a very new young one.
Most of the major pests of turfgrass are bigger. Sod webworm, armyworm, cutworm, grubs.
What kind of grass is this? TTTF?
I think I see a couple square green areas like pieces of sod that are unaffected.
Use a shovel. Check the soil and let us know. Was there an old pool that was filled in here? Sandy spot? High pH?