Stirrups are uniform socks that were commonly worn by baseball players up until the mid-1990s, when major league players began wearing their pants down to the ankles, setting a trend that was soon picked up by players in minor and amateur leagues. Until then, stirrup socks had been an integral part of the traditional baseball uniform, giving them a distinctive look. A high sock was needed since baseball players wore "knickers" which, similar to football pants, came to just below the knee. The stirrup socks served to display team colors, stripes or team logos. For example, for several years the Minnesota Twins wore black stirrups with "TC" on the side, for "Twin Cites". The Houston Astros wore black stirrup socks with a white star on the side. The stirrup sock colors were also the basis of team names, including the Cincinnati Red Stockings (later the "Reds"), Boston Red Sox, and Chicago White Sox. For these reasons, traditionalists lament the recent "sockless" look in baseball uniforms.

Stirrup socks are worn on top of long socks called "sanitaries," usually white in color. This is because early color dyes in the outer stirrup sock were thought to pose health issues, as well as the fact that the inner, less expensive white sock could be changed more frequently. The stirrup sock lacked a foot, instead having a loop ("stirrup") which fit under the foot and exposed part of the white undersock. Over the years, the stirrup loop tended to get longer, exposing more of the white undersock, thus creating a look unique to baseball.

However, by the 1980s many players were pulling the loop so high that only the white undersock and the loop itself showed - the rest of the game sock being hidden by their pants. For many years teams had enforced rules so that uniforms were worn "uniformly", including team socks. For example, Leo Durocher, longtime manager of the Chicago Cubs, had a measuring stick in the clubhouse. Players were required to match the length of their stirrup loops to this stick at about 4 inches, exposing only a small part of the white sanitary. Increasingly lax regulation of uniform codes by Major League Baseball eventually contributed to players ignoring the traditional look.

Although some teams continue to wear traditional baseball stirrup socks, particularly college teams, another option has been to replace the stirrup/undersock with a "2 in 1" combination sock mimicking the real thing, or simply to wear a single solid knee high sock with knickers. The trend back to knickers and high socks is particularly evident among youth and high school teams. A few pro players, such as Brian Tallet of the Toronto Blue Jays and Jamie Moyer of the Philadelphia Phillies have been spotted wearing genuine stirrups recently to much fanfare. The minor league Springfield Missouri Cardinals wear a 2-in-1 version of the traditional St Louis Cardinals' game sock that looks very much like the real thing.

Other sports also use, or have used, stirrup socks, but traditionally wore a white sweat sock over, instead of under, the colored stirrup game sock (eg, basketball, football, hockey). There are still some sock companies manufacturing stirrup socks for baseball and other sports, including Twin City Knitting Company in Conover, North Carolina. Uni Watch Blog, a site that is committed to the "Obsessive Study of Athletics Aesthetics," advocates the use of stirrups in baseball. In fact, Uni Watch's support of the stirrup is so large, a striped stirrup is present in the logo.

One would think that since so many fans like the stirrup look, some teams would start to enforce a strict stirrup policy. I mean, come on, there's not one insignificant detail that people bitch about more than the lack of long socks and stirrups. everyone would love it.