Police use a variety of forms of non-lethal force to end standoffs or disperse unruly crowds. Tear gas and mace are the most commonly used, but police also use non-metal bullets to subdue subjects without causing serious injury.
These projectiles, sometimes called "knee knockers" because of the way they bounce and hit a suspect in the legs, can be made of foam, rubber or wood. Police also fire cloth bags filled with plastic or foam beans.
The projectiles are usually between one and three inches in diameter. A person stuck by a ‘knee knocker' will suffer severe pain directly after being hit and bruising in the affected area, but rarely more serious injuries.