Figure out if you have weeds in your grass by searching your yard for any plants with different characteristics from grass. While grass has long, thin blades and no stems, most weeds have broad leaves that branch off from stiff stems. Look for flowers, because while many weeds produce flowers, grass is not a flowering plant.
Most weeds have broad leaves, but some weeds, such as crabgrass and nutsedge, look very similar to grass. Differentiate crabgrass from regular grass by looking at the plant's leaves, which are similar to grass blades, but broader and less shiny. Crabgrass also grows much more quickly than regular grass, making large, fast-growing clumps of this weed easily identifiable. Remove crabgrass by pulling out as much leaf and root material as possible, as new plants can grow from very small pieces of root.
Nutsedge looks even more like actual grass than crabgrass. Identify this weed by looking at its roots. This plant's name comes from the fact that it grows large tubers that look like nuts. Remove nutsedge by pulling the plant out by hand. While nutsedge is a vigorous weed, it is not as persistent as crabgrass.
Always use gloves when removing broad-leaved weeds, as this group of plants includes common toxic weeds like poison ivy, poison oak and stinging nettle.