Very possible you have some sort of fungii or grass fungus. Usually caused by too much water or overcrowding of trees, shrubs or plants.
It can also come from a lawn mower that was used for mowing someone else's lawn that has this fungus. Lawn fungus can spread very easily from one lawn to another.
Maintenance landscapers need to clean all equipment with soapy water before continuing on to the next lawn.
Dig out a good clump of this grass and take it to your nearest nursery or greenhouse. They should be able to tell you what the problem might be.
Do NOT take it to the nearest big box store as they usually have inexperienced employees.