Echinochloa crus-galli is a species of wild grass originating from tropical Asia that was formerly classified as a panicum grass. It is commonly known as cockspur, cockspur grass, barnyard grass, barnyard millet, water grass, cocksfoot grass, cockshin grass. It is sometimes referred to using the general term, barnyard grass, which may refer to any species of the genus Echinochloa. This plant can grow to 1.5 m (5 ft) in height and has long, flat leaves which are often purplish at the base. Most stems are upright, but some will spread out over the ground. Stems are flattened at the base. The seed heads are a distinctive feature, often purplish, with large millet-like seeds in crowded spikelets.

Considered one of the world's worst weeds, it reduces crop yields and causes forage crops to fail by removing up to 80% of the available soil nitrogen. It acts as a host for several mosaic virus diseases. Heavy infestations can interfere with mechanical harvesting.

Individual plants can produce up to 40,000 seeds per year. Water, birds, insects, machinery, and animal feet disperse it, but contaminated seed is probably the most common dispersal method.