Nutsedge is actually a sedge, not a grass. You can tell from its triangular stem.
Yellow nutsedge thrives under warm, wet conditions and can often be found in low, damp areas of lawns. This weed is often most problematic during summers with above normal rainfall. Management and environmental factors, including improper mowing, insect damage, drought stress, etc., which stress or reduce the density or competitive ability of the desirable turfgrasses, will often lead to increased populations of yellow nutsedge.
Changing your watering habits so the soil isn’t always wet, and having us apply a Liquid Aeration in the spring and fall (or purchasing and applying Aerify Plus yourself) to help loosen the soil will help improve your lawns resistance to nutsedge. Mowing well, and encouraging healthy grass growth will also help. As a last resort, there are chemicals that will kill nutsedge without killing the grass that do help.