Major League Baseball uniforms

The Cincinnati Red Stockings (here pictured in 1882) popularized the adoption of sock color as the explicit identity of the club

The official rules of Major League Baseball require that all players on a team wear matching uniforms, although this rule was not enforced in the early days. Originally, teams were primarily distinguished by the colors of their stockings and the success of the Cincinnati Red Stockings popularized the adoption of sock color as the explicit identity of the club. The 1876 Chicago White Stockings actually wore caps of different colors. In 1882, the National League assigned stocking colors to the member clubs: red for Boston, white for Chicago, grey for Buffalo, blue for Worcester, gold for Detroit, green for Troy, and so on. That year, the league also assigned jersey and cap colors, but by player position rather than by club.

Traditionally, when playing at home, teams wore uniforms that were mostly white with trim in team colors and when playing away, they wore uniforms that were mostly gray with trim in team colors. Aside from the obvious need to distinguish one team from the other, conventional wisdom held that it was more difficult to properly launder uniforms while on a road trip, thus the "road grays" helped to hide accumulated soil. This convention continued well after its original premise was nullified by the issuance of multiple uniforms and the growth of the laundromat industry.

All-time uniforms displayed at the Atlanta Braves Museum in 2009

Starting in the 1970s, with the advent of synthetic fabrics, teams began using more color in their uniforms, notably the Kansas City Athletics in 1963, the San Diego Padres' brown-and-yellow scheme beginning in 1969, and the Houston Astros' rainbow stripes in the mid-1970s. In the late 1970s, the Pittsburgh Pirates began a trend of multiple combinations of differently colored jerseys and trousers and caps (with the options of black, yellow, and white with pin stripes). At one point in the 1970s, the Cleveland Indians had an all-red uniform. From 1976 to 1981, the Chicago White Sox at times had an all-blue uniform, part of a radical style which included a jersey with a large collar, worn untucked – and, for two games in 1976, shorts.

In his comedy routine "Baseball & Football", George Carlin observes that in baseball, as compared to football, the manager is required to wear the same uniform the players do.[2] However, this was actually not true in the early years of the game. Player-managers were common, but non-playing managers whose realm was strictly the dugout often wore business suits, a common occurrence at the time. Retired players who became managers were more likely to continue to wear a baseball uniform (John McGraw, for example), especially if they were also active on the coaching lines; managers often doubled as third-base coach. By the late 1940s, nearly all managers were wearing baseball uniforms. Connie Mack was the last major league manager to wear a suit in the dugout until his retirement in the early 1950s; however, in contrast to the uniform-wearing managers, Mack rarely if ever stepped onto the field during a game; instead he sent uniformed coaches onto the field when a managerial presence outside the dugout was required.

Starting in the 1990s, MLB clubs began heavily marketing licensed goods, such as caps and uniform jerseys to the public and this has resulted in a wide array of uniforms for each team. Now, some teams have not only a basic home uniform and away uniform, but also special "Sunday game" uniforms and uniforms worn only during batting practice and uniforms worn on singular events. From time to time, individual MLB teams have held "Turn Back the Clock Day", regularly scheduled games in which teams donned uniforms in styles their predecessors wore generations earlier (sometimes called "throwback" uniforms), or other antique-style uniforms such as those of Negro league clubs. The Los Angeles Dodgers occasionally use the livery of their original identity as the Brooklyn Dodgers, on special anniversaries or occasions, for example such as in honor of the retirement of Jackie Robinson's uniform number 42 throughout professional baseball (on April 15 – the anniversary of Robinson's MLB debut – entire teams often wear 42). In addition, in 1999, MLB staged "Turn Ahead the Clock Day", in which teams wore uniforms that were built around a "futuristic" theme, including science fiction references, such as the New York Mets being referred to as the "Mercury Mets."

Blake Snell (left) and Wilson Ramos of the Tampa Bay Rays wearing "Mothers' Day" kits in 2018

The result is that it is now often difficult to say which uniform is a team's "official" one. For example, from 1999 to 2006 the Cincinnati Reds wore a variety of caps: all red, red crown and black bill, black crown and red bill, and all black, but since 2007, only the all-red (home) and red crown/black bill (away) are used. In contrast from the pre-1970s era, in which there usually was just one home uniform and one road uniform (with certain exceptions, such as Oakland and Pittsburgh's complex combinations), today choices of what combination of uniform elements are worn are now sometimes left up to players. In some cases, aspects of the uniform that are considered official are rarely worn, such as the New York Mets' blue home cap, with the orange button, which was rarely seen on the field in the years 1998–2012 in favor of an "alternate" black-and-blue cap. The Mets added the orange button on their blue caps in 1995. Through 2014, the New York Yankees and Los Angeles Dodgers wear uniforms which have changed little since the 1930s – while the Detroit Tigers have worn essentially the same home uniform during that span (only the Tigers, Yankees, Chicago White Sox, and Washington Nationals retain the once-common practice of placing the cap insignia on their home whites, though many teams, including the Nationals and White Sox, do so on alternate jerseys), their road grays have changed more often. The Dodgers (a blue jersey once in 1999) and Tigers (a navy jersey twice in 1995) had worn alternate uniforms in the past, but as of 2010 did not have one (the St. Louis Cardinals didn't wear an alternate jersey until 2013, but since 1998 used an alternate cap, with the distinctive "birds-on-bat" logo rather than the traditional interlocking StL, for some home games, and also in 2013, with the adoption of their home red cap as their full-time standard, the navy blue road cap was designated as an alternate, worn exclusively against red-capped home teams).

Kansas City Royals alternate uniform (left) with the team name on the chest; the away version (right) features the city of origin

Typically, home uniforms feature the team's nickname, while away uniforms feature the name of the team's geographic designation. Currently, the Tampa Bay Rays, Los Angeles Angels, Philadelphia Phillies and St. Louis Cardinals are the only exceptions to this rule, although the Cardinals' aforementioned 2013 alternate placed "St. Louis" on their jerseys for the first time since 1932. These teams feature the club nickname on both the home and away uniforms (since 1900, in 169 seasons – including the Athletics' presence in the city from 1901 to 1954 – the full word "Philadelphia" has never appeared on a Major League jersey). The Milwaukee Brewers did not display their city name on their road gray jerseys from 2000-2019, and from 2000–09, had an alternate blue jersey with "Brewers" on the front. They introduced a navy blue jersey with "Milwaukee" on the front in 2010, but kept the navy alternate with "Brewers" on the front; both navy jerseys were worn interchangeably at home and on the road for the next 10 seasons.. The Brewers redesigned their uniforms for 2020, with "Milwaukee" on the front of the road grays for the first time since 1999.

From 1973 to 2008, the Baltimore Orioles were part of this group – the omission of the city's name being part of a largely successful effort to attract fans from the Washington, D.C. area – before returning "Baltimore" to the road jerseys in 2009, by which time the current Nationals franchise had begun playing Washington, D.C. In 2014, the Los Angeles Dodgers and Chicago Cubs partially joined this group, carrying one road jersey with the city name and another with the team name, and wearing both interchangeably; in only the third game of the season, one player accidentally played the first inning in the "Chicago" jersey while the team wore "Cubs"; the Cubs dropped the alternate road jersey in 2016, leaving the "Chicago" version as the lone style.

As of 2020, only one team wears their city/state name on their home uniforms, the Miami Marlins. From 2009-2019, the Texas Rangers wore their state name on all of their jerseys, but introduced a new uniform set for 2020 to coincide with the move to Globe Life Field which displays "Rangers" on the white jersey.

A number of teams do not display their team nickname on their home uniforms. Instead, they place the team logo or insignia in front. The most famous example is the New York Yankees' classic pinstripe home uniforms featuring the interlocking "NY" logo. Other examples include the Detroit Tigers' Old English "D", and the "Curly W" of the Washington Nationals (the logo was originally used by the Washington Senators).

MLB jerseys worn on the field have been made out of double-knit polyester since the early 1970s. The Pittsburgh Pirates were the first to switch when they opened Three Rivers Stadium following the 1970 All-Star Game. The Cardinals followed suit to open 1971, and the Orioles made a gradual change until adopting them full-time for that season's ALCS.

Sixteen teams debuted double-knits to open 1972; the Red Sox adopted them after the All-Star Game, and the Giants debuted them at home only at mid-season as well. The final flannel holdouts, the Expos, Royals and Yankees, converted to open 1973.

Jerseys have featured an MLB logo on the back collar since 2000, whereas MLB on-field caps have featured an MLB logo on the back since 1992.[3] Until 2007, MLB caps were made out of wool, with a gray underbrim having become common by the late 1980s. (The New York Yankees were among the last MLB teams to wear caps with the previously common kelly green underbrim, only switching their caps to the gray underbrim in 1994.) In 2007, all standard MLB caps were made of polyester, with a black underbrim to reduce glare.

Jersey numbers were first used in Major League Baseball by the Cleveland Indians June 26, 1916. The Indians were inspired by football and hockey teams using numbers. The team donned the numbers on their sleeve and only did so for a few weeks as an experiment.

Jersey numbers would not return again to the Major Leagues until 1923 when St. Louis Cardinals' manager Branch Ricky decided to add numbers to the sleeves on a recommendation by sportswriter John Sheridan. The team was subject to criticism for wearing numbers on their uniforms by opposing teams and fans. Ricky was quoted as saying, "The effect upon the team was bad and ‘busted up’ the team morale or spirit completely. They really didn’t want to show themselves on the field. Because of the continuing embarrassment to the players, the numbers were removed." Jersey numbers fell out of use again until 1929.

In 1929, the Cleveland Indians and the New York Yankees both introduced jerseys with numbers on the back. On April 16, 1929 the Yankees opening game was cancelled due to rain while the Indians played, becoming the first team to wear numbers on the back. By the mid-1930s every team in Major League Baseball team were wearing numbers on the back of jerseys except the Philadelphia Athletics. The Athletics later added numbers to their jerseys in 1939.[4]

The first jersey number retired by a team was #4 by the New York Yankees to honor Lou Gehrig. In 1997, MLB retired Jackie Robinson's #42 league wide, the first and only number that no player is allowed to wear anymore. As of April 15, 1997 #42 was retired except for players wearing the number prior to it being retired. Mariano Rivera was the last player to wear #42 when he retired in 2013. Every April 15 since 2009 every player, manager, and umpire wears #42 to commemorate Jackie Robinson. April 15 is now known as Jackie Robinson day.[5]