Game played by teams of players on horseback. Players use mallets with long flexible handles to drive a wooden ball through goalposts. It was first played in Persia in the 6th century BC; from there it spread to Arabia, Tibet (polo is Balti for ball), South Asia, and the Far East. The first British polo clubs were formed in India in the mid-19th century; the game came to the U.S. a few decades later. Polo has long been primarily played by the wealthy, because of the expense of acquiring and maintaining a stable of polo ponies (actually full-sized adult horses, bred for docility, speed, endurance, and intelligence). The standard team is made up of four players whose positions are numbered 1–4. A game consists of six 7.5-minute periods called chukkers or chukkas. The field is 300 yards (274.3 m) long by 160 yards (146.3 m) wide; an indoor version of the game is played on a smaller field.