Either your soil is too fertile, or the plant is just going through a shock, either to climatic shift, soil, watering, or root shock. Is the crown of the grass slightly above the soil line? That plays an important role, as sometimes composted soil or bark mulched soils that are spread around the crown too heavily and deeply, the crown slowly rots and then over- watering becomes a problem. Grasses as a whole do not need a very fertile soil to grow, just making sure drainage and aeration are not compromised.