What kind of sporting event is divided into chukkas?

Polo is a team sport played on horseback. The objective is to score goals against an opposing team. Players score by driving a small white plastic or wooden ball into the opposing team's goal using a long-handled mallet. The traditional sport of polo is played on a grass field up to 300 by 160 yards (270 by 150 m). Each polo team consists of four riders and their mounts.

The modern game lasts roughly two hours and is divided into periods called chukkas (occasionally rendered as "chukkers"). Polo is played professionally in 16 countries. It was formerly an Olympic sport.

Polo is now an active sport in 77 countries, and although its tenure as an Olympic sport was limited to 1900–1939, in 1998 the International Olympic Committee recognized it as a sport with a genuine international governing body, the Federation of International Polo. The World Polo Championship is held every three years by the Federation of International Polo.

Polo is, however, played professionally in only a few countries, notably Argentina, Australia, Brazil, Canada, Chile, Dominican Republic, France, Germany, Iran, India, New Zealand, Mexico, Pakistan, Jamaica, Spain, Switzerland, the United Kingdom, and the United States. Polo is unique among team sports in that amateur players, often the team patrons, routinely hire and play alongside the sport's top professionals.