Inbaseball, theuniform number is a number worn on the uniform of each player and coach. Numbers are used for the purpose of easily identifying each person on the field as no two people from the same team can wear the same number.^[a] Although designed for identification purposes only, numbers have become the source of superstition, emotional attachment, and honor (in the form of a number retirement). InMajor League Baseball, player andmanager numbers are always located on the back of the jersey. A smaller number is often found on the front of the jersey, whileumpires wear their numbers on the uniform shirt sleeve.

According to common tradition, single-digit numbers are worn byposition players but rarely bypitchers, and numbers 60 and higher were rarely worn at all until the 2010s.^[1] Higher numbers are worn during spring training by players whose eventual place on the team is uncertain; they are also sometimes worn during the regular season by players recently called up from theminor leagues. However, such players usually change to a more traditional number once it becomes clear that they will stay with the team.^[1] These traditions are not enforced by any rule,^[2] and exceptions are common. Examples of star players wearing numbers higher than 60 includeCarlton Fisk (72),^[b]Kenley Jansen (74), andAaron Judge (99).^[1] In 2018,Blake Snell became the first pitcher wearing a single-digit number (4) to appear in theAll-Star Game and the first to win theCy Young Award.^[3]

The idea of assigning numbers to players was first proposed as a means of allowing spectators to more easily identify each player on the field. The practice of numbering competitors in other sports was already decades old when, in 1894, an unnamed individual suggested to James Hart, president of theChicago Colts, that his players should wear uniform numbers.^[4] On December 29, 1894, theSt. Louis Post-Dispatch wrote of theNational League club: "Every one who has attended a ball game knows how puzzled one occasionally gets in endeavoring to recognize some player or trying to locate a man who is on the team, but whose position has been changed from that signified on thescore-card. The plan suggested to Mr. Hart is very simple. It is for every man on the team to have a separate number, which he shall keep throughout the season....On the score-cards, the names of the players, with their numbers, shall be printed; and in this way the spectator can readily identify any player on the field."^[4] However, there is no record of the Colts implementing the suggestion.

In 1906, the team, which had since been renamed theChicago Cubs, devised a uniform numbering system in which, rather than sewing numbers onto jerseys, each player's number would be printed next to their name on the game's scorecard.^[4] Within this system, which was also adopted by other teams over the next few years, stadium scoreboards would display the team's lineups in numerical form. In order to determine the players corresponding to the numbers on the scoreboard, fans in attendance would have to buy the scorecard. Teams frequently changed player numbers in order to render previous scorecards unusable.^[4] By 1911, the system was employed by both Chicago teams, the Cubs and theWhite Sox, as well as theBoston Braves,Boston Red Sox,Cleveland Indians,Detroit Tigers,Pittsburgh Pirates, andWashington Nationals.^[4]

The earliest official record of numbers being physically placed onto uniforms is from 1907, when the Reading Red Roses of the Atlantic League numbered player jerseys in an effort to help fans identify them. While it is unknown if the team ever took the field with numbers, theNational Baseball Hall of Fame and Museum cites the Red Roses as the first team verified to have numbered their players.^[5] The earliest photographic evidence of a baseball uniform number dates back to 1909. In an issue of theChicago Daily News, star pitcherJosé Méndez, then playing for theCuban Stars, a travelingNegro league baseball team of the early 1900s, is seen wearing the number 12 on his left sleeve.^[5]

The first time that a Major League team wore numbers was on June 26, 1916.^[c] Inspired by the usage of numbers infootball andhockey, the Cleveland Indians added large numbers to their left sleeves for a game on theirhome field. This experiment was tried for a few weeks, then again the next season, before being abandoned.^[5] In 1923, theSt. Louis Cardinals adopted uniform numbers on their sleeves. However, as then-managerBranch Rickey recalled, the now-easily identifiable players were "subjected to field criticism from the stands and especially from opposing players,"^[5] so the numbers were removed. Other clubs to experiment with uniform numbers on their sleeves in 1923 include theIndianapolis ABCs of theNegro National League and theSan Antonio Bears of theTexas League.^[5]

In 1929, both the Indians and theNew York Yankees were planning to start the season with uniform numbers on the back of the jersey. Both teams were scheduled to begin their seasons on April 16, however, a rainout forced the Yankees to postpone their season opener. The Indians played their game as scheduled, in the process becoming the first major league team to wear uniform numbers on the back of the jersey.^[5] The practice of adding uniform numbers to home and road jerseys became universal in theAmerican andNational Leagues in 1937, when thePhiladelphia Athletics became the last team to do so.^[5][7]

In 1951, theSpringfield Cubs of theInternational League pioneered the concept of placing numbers on the front of the jersey.^[5] A year later, theBrooklyn Dodgers incorporated the idea as well.

Today, numbers on the front are common at all levels of play. In 1940, theMemphis Red Sox of theNegro American League wore numbers on their pants. The idea was also incorporated by theHouston Astros from 1975 to 1978, placing the number on their left hip. TheChicago White Sox also wore left hip numbers from 1982 to 1989.^{[citation needed]}

Until 2022, thePhiladelphia Phillies were the only Major League team to wear a number on the sleeve of their jerseys; it was removed to eventually see it replaced by a sponsorship patch fromIndependence Blue Cross, in line with the rest of the league. The White Sox did so from 1971 to 1975, and theSt. Louis Cardinals did in 1979 and 1980.^{[citation needed]}

The official rules of baseball state that uniforms must be identical for all members of a team. The only mention of uniform number is that it must be on the back and a minimum of six inches tall.^[8] Each player must have their own unique number, but there is no rule requiring coaches to have unique numbers. For example, in 2015,Alan Trammell (who wore number 3 for his lengthy career as aDetroit Tigers player and manager) returned to coach first base and wore 3 again, despite the number belonging toIan Kinsler at the time, marking a rare instance of a coach sharing a number with a player.^[9]

In their first career games,Cincinnati Reds outfielderEric Davis andChicago White Sox pitcherJoe Horlen did not have jersey numbers. Both of these players were just called up to the big league team while it was on the road and the only uniform available had no number.

On September 27, 1999,Detroit Tigers center fielderGabe Kapler took the field donning a numberless uniform. That day, the Tigers played their last game at historicTiger Stadium and, in honor of great Tigers of the past, members of the starting lineup wore the uniform numbers of corresponding members of an All-Time Detroit Tigers team voted on by the fans. Since Kapler played center field, he was to wearTy Cobb's uniform number, but since Cobb played before numbers were used, Kapler's back was blank.^[10]

For the 100th anniversary ofFenway Park on April 20, 2012, theBoston Red Sox and New York Yankees wore 1912-style uniforms which had no numbers.^[11]

OnJackie Robinson Day, teams across MLB all wear uniform number 42 to honor him.^[12] [See "Retired numbers," below.] The MLB has taken this tribute so far that, on that day only, all 30 team websites' active rosters say that every player on the team is number 42.

On August 21, 2012, the Boston Red Sox played their first home game since the death ofJohnny Pesky, and all players wore his retired number 6 jersey during the game.^[13]

On September 26, 2016, the Miami Marlins played their first home game since the death ofJose Fernandez, and all players wore his number 16 jersey during the game.

On July 12, 2019, the Angels played their first home game since the death of pitcherTyler Skaggs, and all players wore his number 45 jersey during the game. After the game, acombined no-hitter, the players removed their Skaggs jerseys and laid them around the mound to honor his memory.

On September 9, 2020, all players and field coaches of thePittsburgh Pirates woreRoberto Clemente's number 21 in his honor. A number ofPuerto Rican MLB players, as well asMilwaukee Brewers pitcherBrent Suter, also wore number 21 in honor of Clemente. Beginning in September 2021,Latin American players andRoberto Clemente Award winners were given the option to wear number 21 during Roberto Clemente Day.

The original baseball numbers were based on the lineup. The starting players would be numbered 1-8, based on their spot in the order. The backup catcher would be number 9, and the pitchers would wear 10-14 (but not 13, as it is considered unlucky).^[14] Notable examples of this system are teammatesBabe Ruth (he was number 3 and batted third for the Yankees) andLou Gehrig (number 4, batted fourth).

Several teams experimented with numbering-by-position during the 1930s. In1939, theCincinnati Reds, undergeneral managerWarren Giles,^[15] introduced what would be thelongest-lasting convention, in which pitchers customarily wore numbers between 30 and 49; outfielders between 20 and 29; infielders between 10 and 19; and catchers, coaches and managers in the single digits—with the manager often sporting number 1. (An exception briefly occurred in the early 1950s, when Cincinnati's coaches and managers were assigned numbers in the 50s.)^[16]

TheNew York Giants adopted this system in1947, and when Giles became chief executive of theNational League in 1952, many other NL clubs began to follow suit. TwoAmerican League teams, thefirst season of theexpansionLos Angeles Angels and theCleveland Indians beginning in1963, also adopted the numbering scheme.^[16]

In his1969 memoir,Ball Four, pitcherJim Bouton tells how he asked his new NL team, theHouston Astros, for his traditional number 56 (which he had worn with both theNew York Yankees and theSeattle Pilots), but was assigned44 instead because of the Astros' numbering custom. Bouton wrote: "I asked if there was any chance I could get 56. [The equipment manager] said he didn't think so, that all our pitchers have numbers in the 30s and 40s. He said I'd have to talk to [general manager Spec]Richardson or managerHarry Walker if I wanted to change the rule. I said I was sure they wouldn't want to be bothered with something so small, and he said, 'Oh, you'd be surprised.' Oh no I wouldn't."^[17]

However, the number-by-position convention was never a formal rule, although one was proposed by Giles at the 1958 Winter Meetings.^[15] Moreover, a few National League clubs — notably theDodgers — consistently resisted the idea. The custom was slowly abandoned during the 1970s and 1980s. (In fact, in1970, the Astros assigned Bouton his traditional number 56.)

Despite today's MLB teams no longer assigning numbers solely by a predefined systems, some trends regarding player numbers include the following:

• Uniform numbers are either one or two digits - no MLB player has ever worn a number of three or more digits. Numbers used arepositive,whole, andrational, except in one specific special case:Eddie Gaedel, a little person who made one plate appearance for theSt. Louis Browns as a publicity stunt in 1951, wore the fractional number1⁄8.^[18]
  • Players in theDevelopmental Player System ofNippon Professional Baseball's (NPB), the Japanese Major Leagues, are required to wear a three-digit number with either a leading 0, 1, or 2 (e.g.: 101, 001, or 201); these are developmentalpractice squad players who may only play in NPB's minor leagues, theEastern League andWestern League.^[19][20]
• Pitchers traditionally wear higher numbers and do not typically wear single-digit numbers.^[1][21] This was particularly true from the 1950s through the 1980s, when single-digit uniform numbers for pitchers were virtually never used. Since then, a pitcher sporting a single-digit number has become less rare.
• Numbers 60 and above have historically been rarely worn in the regular season. Duringspring training, such high numbers are often given to players who are perceived as unlikely to make the regular-season team. It is generally thought that the higher the number, the less chance of making the team.^[22] However, as rosters expand, as more low numbers are retired, and as players adopt high numbers as a means of self-expression,^[1] uniform numbers in the 60s or higher are becoming increasingly common. As many as 292 MLB players wore a uniform number in the 60s or 70s during the 2024 season; all but 30 were pitchers.^{[citation needed]}
• Number 49 is traditionally sought out byknuckleball throwing pitchers:^[23] notable examples includeHoyt Wilhelm,Charlie Hough,Tim Wakefield, andTom Candiotti.
• In Japan's NPB, number 18 is often reserved for the ace pitcher.^[24] Upon arriving in MLB, Japanese "import" pitchers have sought the number again (includingHiroki Kuroda,Daisuke Matsuzaka,Hisashi Iwakuma,Kenta Maeda,Yusei Kikuchi, andYoshinobu Yamamoto).
• Numbers 0 and 00 are uncommon, but have been used by several players.^[1] The New York Yankees, whose single-digit numbers higher than zero have all been retired, had in the past resisted issuing the number zero to a particular player, but would finally do so in 2019 when they signedAdam Ottavino, who has worn the number for all but two Major League seasons.^[25]

• Numbers 01 through 09 (with a leading zero) are some of the rarest numbers that have been worn. CatcherBenito Santiago wore 09 for the San Diego Padres andFlorida Marlins.^[26] He did so because the chest protector strap on the back of his catching gear would otherwise run across a single digit,^[27] obscuring the numeral, along with its thicker material layered with the strap and latch irritating him physically.^[28]
• In honor ofRoberto Clemente, players fromPuerto Rico generally do not wear number 21.^[29] However, some Puerto Ricans such asCarlos Delgado andRubén Sierra have chosen to wear the number for the same reason.^[30]

Players in the modern game have been moving away from traditional numbering conventions. Number choices are increasingly varied. Paul Lukas noted that the increasing use of higher numbers in baseball could be traced to the iconic status of certain high numbers in hockey, most notablyWayne Gretzky's 99 andMario Lemieux's 66. As of August 2019^[update], nearly four times as many players had worn 99 in the 21st century (15) than in all of the 20th century (4), and nearly as many players had worn 0 in the 21st century (10) as in the 20th (11).^[1] Every two-digit number has been worn during a regular-season MLB game, with number 89 the last to be used—it was first worn during 2020, byMiguel Yajure of the Yankees.^[31] In 2024, every jersey number between 00 and 99 (aside fromJackie Robinson's retired 42) was used during the season for the first time.^[32]

If a player who grows superstitious about or emotionally attached to a certain number changes teams, he will occasionally bargain for the right to wear the number if it is already in use on his new team. In 1993, whenRickey Henderson joined theToronto Blue Jays, he paid Turner Ward $25,000 for the number 24, which he wore at various points throughout his career.^[33][34] Before the 2005 season, upon joining theAtlanta Braves for a second stint,Brian Jordan gave third base coachFredi González aHarley Davidson motorcycle in exchange for number 33, whileJuan Pierre bought a motorcycle for managerGrady Little in exchange for the number 9 on theLos Angeles Dodgers in 2007.^[35] In a less lucrative transaction, whenMitch Williams joined thePhiladelphia Phillies in 1991, he bought number 28 fromJohn Kruk for $10 and two cases of beer.^[33]

Some players who are unable to acquire the number they had on their previous team will obtain a similar number. For example,Roger Clemens wore number 21 for over 15 years while pitching for theUniversity of Texas, theBoston Red Sox, and the Blue Jays. When he joined theNew York Yankees prior to the 1999 season, Clemens asked long-time Yankee outfielderPaul O'Neill to surrender the number. O'Neill refused, so Clemens chose number 12, the reverse of 21, then settled on number 22, which he wore for the remainder of his career.^[36] After a stint with his hometownHouston Astros, Clemens resigned with the Yankees for the 2007 season, promptingRobinson Canó to change numbers from 22 to 24 in anticipation of the signing.^[37]

PitcherJoe Beimel wore number 97 throughout his career because his first child was born in 1997.^[38] During the 2006 season, while playing for the Red Sox,J. T. Snow wore number 84 to honor his fatherJack, a formerNational Football Leaguewide receiver who had died earlier in the year.^[39]

For some players, an oddity or coincidence has provided an opportunity to express something about themselves with their number. In 1951, while playing for the minor-leagueFargo-Moorhead Twins, Johnny Neves wore the number 7 backwards on his jersey because "Neves" is "seven" spelled backwards.^[5]Bill Voiselle, who had grown up inNinety Six, South Carolina, wore number 96 from 1947 to 1950 to honor his hometown.^[5] At the time, this was by far the highest number ever worn in Major League Baseball, and Voiselle had to seek special league permission in order to wear it.^[40]Carlos May, who was born on May 17, wore number 17, meaning that his jersey read both his name and number and his birthday ("May 17").^[5]Eddie Gaedel, a little person who made one plate appearance for theSt. Louis Browns as a publicity stunt in 1951, wore the number1⁄8.^[41]

Players,managers,coaches, or other figures with notable contributions to a given team will sometimes have their uniform numberretired such that the number is never reissued by that team. Only the individual with the retired number can wear that number upon a potential return to that team. Generally, such retirements are reserved for those individuals whose performance and impact were notable not just to a single team, but toMajor League Baseball as a whole.

The first MLB number retired wasLou Gehrig's #4 by theNew York Yankees. Aretirement ceremony was held in his honor atYankee Stadium on July 4, 1939.^[42] However,Babe Ruth's famous #3 uniform remained in circulation from the day he was unconditionally released by the Bombers, February 26, 1935, until its formal retirement on June 13, 1948, when a mortally ill Ruth attended the 25th anniversary celebration ofYankee Stadium—nicknamed "The House That Ruth Built"—just 64 days prior to his death from cancer at age 53.^[43] It had been worn in the interim by seven players,George Selkirk (1935–1942),Bud Metheny (1943–1946),Roy Weatherly (1946),Eddie Bockman (1946),Frank Colman (1946–1947),Allie Clark (1947), andCliff Mapes (1948), with rookie outfielder Mapes switching jerseys to #13 for the remainder of1948.^[44]

As of 2024, MLB has seen at least one number retirement in each season since 1982. #20 has been retired by 11 teams, more than any other number (excludingJackie Robinson's #42, which has been retired by all teams). The lowest positive number not retired by any team is 38, while the highest player uniform number to be retired isCarlton Fisk's #72, which he wore with theChicago White Sox. Two numbers higher than 72 have been retired. TheSt. Louis Cardinals retired #85 in honor of their then-ownerAugust Busch Jr. in 1984, with that number chosen to signify his age at the time of its retirement.^[45] TheCleveland Guardians (then Indians) retired #455 in 2001 to honor their fans and commemorate the then-MLB record home sellout streak of 455 games.^[46][d]

Ten players^[e] and two managers^[f] have had their numbers retired with two teams.Ralph Kiner had his number retired for his contributions as a player for thePittsburgh Pirates and as a broadcaster for theNew York Mets.^[g]Frank Robinson's #20 is retired by three teams: theOrioles andReds for his contributions as a player and theGuardians for his contributions as a player and manager.^[h]Nolan Ryan had two different numbers (#30 and #34) retired among three teams: theAngels,Rangers, andAstros. The other individuals to have multiple numbers retired are Sparky Anderson (#10 with theReds and #11 with theTigers), Wade Boggs (#12 with theRays and #26 with theRed Sox), Carlton Fisk (#27 with theRed Sox and #72 with theWhite Sox), Roy Halladay (#32 with theBlue Jays and #34 with thePhillies), and Reggie Jackson (#9 with theAthletics and #44 with theYankees).

The Yankees have retired more numbers than any other team (22 numbers honoring 23 of their former players, plus #42 for Jackie Robinson, who did not play for the team), including all non-zero single digit numbers.^[47] TheMiami Marlins are the only team with no retired numbers as of September 2024, however, the team has retired and unretired the #5. It was initially retired in 1993 in honor ofCarl Barger, who had died in December 1992.^[48] Barger was the president of the then-expansion franchise and thus never wore a number for the team. The number, initially chosen because it had been worn byJoe DiMaggio, Barger's favorite player,^[48] was returned to circulation in 2012 when the Marlins moved into theircurrent stadium. Instead of a retired number, a plaque honoring Barger was placed at the new stadium.^[49] The #5 was also unretired by theCincinnati Reds, who initially retired it to honorWillard Hershberger, an active player who committed suicide in 1940,^[50] but placed it back into circulation at the end of the season. The number was later permanently retired by the team to honor the contributions ofJohnny Bench.

In 2021, afterRoberto Alomar was banned from baseball following an independent investigation into allegations of sexual misconduct, theToronto Blue Jays announced that he would be removed from theirLevel of Excellence and that his retired number banner would be taken down.^[51] Alomar's #12 was unretired upon being assigned toJordan Hicks during the 2023 season.^[52]

The only other cases of retired numbers being returned to circulation by an MLB franchise occurred when theMontreal Expos moved to Washington, D.C. and became theWashington Nationals. At the time, the Expos had retired three numbers to honor four former players.^[i] All were returned to circulation by the Nationals.^[53]

In 1997, for the first and thus far only time, a number was retired throughout Major andMinor League Baseball.^[54] The #42 cannot be issued by any team, having been retired in honor ofJackie Robinson.^[j] Those wearing the number upon its league-wide retirement, such asMo Vaughn of theBoston Red Sox andButch Huskey of theNew York Mets, were allowed to keep it under agrandfather clause.^[54] The last person to wear #42 in the Major Leagues wasMariano Rivera of theNew York Yankees, who retired following the 2013 season; the last person to wear #42 in Minor League Baseball was Art Silber, owner of and occasional coach for thePotomac Nationals until his retirement from coaching in 2012.^[55]

However, the #42 would be worn by several players other than Rivera in2007, which marked the 60th anniversary of Robinson's first MLB appearance (an event that broke the sport's20th-century color line). Before the season, then-Cincinnati Reds outfielderKen Griffey Jr. asked Robinson's widow,Rachel Robinson, and MLB CommissionerBud Selig for permission to wear #42 on April 15, the anniversary date of Robinson's historic game,^[56] which was formally namedJackie Robinson Day by MLB in 2004.^[57] Both gave their approval, and Selig later allowed any player to wear #42 on Jackie Robinson Day. In response, over 200 players elected to do so, including six teams that opted for all of their players to participate.^[56] Since 2009, all players and coaches on all teams, as well as all umpires, have worn #42 on Jackie Robinson Day.^[58]

In 1970, National League umpires first wore identifying numbers on the right sleeve of their shirt or coat. The numbers were assigned in alphabetical order and remained this way through 1978, meaning umpires could, and often did, wear a different number from year to year. In 1979, NL umpires chose numbers based upon seniority, and that system remained through 1999, the last season of separate umpiring staffs for the National and American Leagues.

American League umpires did not wear identifying numbers until 1980. Unlike the NL, there were no set rules for number assignments.

When the AL and NL umpiring staffs merged in 2000, the senior umpire who wore a given number could keep that number, while the junior umpire had to select a new number.

Since 2020, MLB has allowed three-digit numbers on umpires, but the procedure applies to reserve umpires (call-up umpires when regular umpires are on vacation).

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