Boxing is a combat sport where two opponents fight within a roped square ring. They use gloves to hit each other while avoiding blows, competing over a series of timed rounds with breaks in between. The sport originated in ancient Greece and grew popular among working classes in the 18th-19th centuries. Standard rules were established in the mid-19th century, requiring gloves and limiting rounds. Boxing remains controversial due to its violence but is internationally popular, especially certain heavyweight champions from the United States in the 20th century.