Cricket is one of many games in the "club ball" sphere that basically involve hitting a ball with a hand-held implement; others include baseball, golf, hockey, tennis, squash, badminton and table tennis. In cricket's case, a key difference is the existence of a solid target structure, the wicket (originally, it is thought, a "wicket gate" through which sheep were herded), that the batsman must defend. The cricket historian Harry Altham identified three "groups" of "club ball" games: the "hockey group", in which the ball is driven to and fro between two targets (the goals); the "golf group", in which the ball is driven towards an undefended target (the hole); and the "cricket group", in which "the ball is aimed at a mark (the wicket) and driven away from it".
Crickets are kept as pets and are considered good luck in some countries; in China, they are sometimes kept in cages or in hollowed-out gourds specially created in novel shapes. The practice was common in Japan for thousands of years; it peaked in the 19th century, though crickets are still sold at pet shops. It is also common to have them as caged pets in some European countries, particularly in the Iberian Peninsula. Cricket fighting is a traditional Chinese pastime that dates back to the Tang dynasty (618–907). Originally an indulgence of emperors, cricket fighting later became popular among commoners. The dominance and fighting ability of males does not depend on strength alone; it has been found that they become more aggressive after certain pre-fight experiences such as isolation, or when defending a refuge. Crickets forced to fly for a short while will afterwards fight for two to three times longer than they otherwise would.
More than 900 species of crickets are described; the Gryllidae are distributed all around the world except at latitudes 55° or higher, with the greatest diversity being in the tropics. They occur in varied habitats from grassland, bushes, and forests to marshes, beaches, and caves. Crickets are mainly nocturnal, and are best known for the loud, persistent, chirping song of males trying to attract females, although some species are mute. The singing species have good hearing, via the tympana on the tibiae of the front legs.