It is most associated with those who play baseball. However, the baseball cap is far more than just a part of baseball players' uniforms; it is arguably the most popular style of hat in the United States and many Western nations, as well as Japan.
In many ways, the baseball cap is a symbol of the 20th century, as it became popular as the culture of sports increased in popularity, starting (naturally) with baseball. In 1860, the Brooklyn Excelsiors wore the ancestor of the modern, rounded-top baseball cap, and by 1900, the "Brooklyn style" cap became popular. During the 1940s, latex rubber became the stiffening material inside the hat and the modern baseball cap was born.
Baseball caps are made of all types of material and shaped in various styles for different purposes. Major league baseball players wear classic-style caps made of wool with their team's simple logo and colors; the logo is usually embroidered into the wool. Caps used by players commonly have sunglasses attached to the peak that can be flipped down when the player must look into the sky, but kept flipped up at other times.
Athletes in other sports wear caps with their team's logo and colors as "sideline" caps; both types are also sold as authentic team merchandise in retail stores and are quite popular. Other caps may simply have a company's logo, such as Nike or Carhartt; these hats are often made of brushed cotton. Golfers tend to prefer the visor form of cap which doesn't cover the head but keeps the sun out of their eyes; women also traditionally have worn visors casually but a trend towards certain youth subcultures see an increase in visor popularity among both sexes.
Farmers and migrant workers might be seen wearing plastic mesh caps with foam fronts with a farm feed supply company logo or the like printed on the cap. This style of baseball cap is sometimes called a "trucker cap" because of its blue collar associations.
The baseball cap of the New York Yankees may be the most popular sports team cap and comes in many colors (including the classic navy blue) and varieties. Major athletic cap manufacturers include Nike and New Era.
Beginning in the 1980s, the baseball cap also came be associated with film directors, especially Spike Lee and Michael Moore, replacing the beret in the popular image.
Wearing a baseball cap with the peak at certain directions can have significance to gang members, as well.
The idea of wearing the cap backwards is commonly attributed to catchers, when they began using facemasks, as they had to turn the cap around to fit the mask on.