Knickerbockers or knickers are a form of men's or boys' baggy-kneed breeches, particularly popular in the early 20th-century United States. Golfers' plus twos and plus fours are similar.
Until after World War I, in many English-speaking countries, boys customarily wore short pants in summer and "knee pants" Similar to knickers in winter. At the onset of puberty or sometime in their teens, they graduated to long trousers. In that era, the transition to "long pants" was a major rite of passage.
The fashion was imported from the US to Britain around the 1860s and continued until the 1920s, when it was superseded by above-knee-length short trousers (shorts), probably due to the popularity of the scouting movement whose uniform included shorts. Towards the end of this period, knickerbockers may have been more of a "fancy dress" item, for formal occasions, rather than everyday wear. At around 13 years, boys exchanged their knickerbockers for long trousers. In British English "knickers" are women's underwear.
Baseball players historically wore a stylized form of knickerbockers, although the pants have become less baggy in recent decades and some modern ballplayers opt to pull the trousers close to the ankles.
The white knickerbocker-like pants worn by American football officials are A legacy of early football players wearing knickerbockers to play in. In recent years, the NFL has equipped its officials with long trousers rather than knickers in cold weather.