In baseball, the bullpen (or simply the pen) is the area where relief pitchers warm-up before entering a game. A team's roster of relief pitchers is also metonymically referred to as "the bullpen". These pitchers usually wait in the bullpen if they have not yet played in a game, rather than in the dugout with the rest of the team. The starting pitcher also makes his final pregame warm-up throws in the bullpen. Managers can call coaches in the bullpen on an in-house telephone from the dugout to tell a certain pitcher to begin his warm-up tosses.
Each team generally has its own bullpen consisting of two pitching rubbers and plates at regulation distance from each other. In most Major League Baseball parks, the bullpens are situated out-of-play behind the outfield fence. There are currently two MLB parks with bullpens in playable foul territory: Oakland Coliseum and Tropicana Field.
The origin of the term bullpen, as used in baseball, is debated, with no one theory holding unanimous, or even substantial, sway. The term first appeared in wide use shortly after the turn of the 20th century and has been used since in roughly its present meaning. According to the Oxford English Dictionary the earliest recorded use of "bullpen" in baseball is in a Cincinnati Enquirer article published on May 7, 1877, in which writer O.P. Caylor noted in a game recap:
"The bull-pen at the Cincinnati grounds with its `three for a quarter crowd' has lost its usefulness. The bleacher boards just north of the old pavilion now holds the cheap crowd, which comes in at the end of the first inning on a discount."
Though conditions were initially a vast improvement over Richmond detention centers, problems grew in proportion to the number of inmates. By late summer 1864, the prison population made Andersonville one of the largest cities in the Confederacy. At its peak in August, the "bullpen", built to lodge up to 10,000 enlisted men, held 33,000 grimy, gaunt prisoners, each one crammed into a living area the size of a coffin. Their only protection from the elements were "shebangs", hand built shelters low to the ground created by driving forked branches into the sandy soil four to eight feet apart and a piece of limb laid in the two forks creating the center pole. Planks or limbs were laid from the center pole to the ground creating what is also known as a "lean-to". The planks or limbs were covered with tent shelter halves, gum sheets, overcoats, or blankets as the owner could afford. If no woven material was available, then the shelter was covered in broad leaves giving the owner some shade but little protection from the rain.
This wartime usage in the United States has occurred as recently as World War II. Tokio Yamane described conditions in Japanese relocation camps, referring to a "bull pen" within a stockade at Tule Lake, California.
Prisoners in the stockade lived in wooden buildings which, although flimsy, still offered some protection from the severe winters of Tule Lake. However, prisoners in the "bull pen" were housed outdoors in tents without heat and with no protection against the bitter cold. The bunks were placed directly on the cold ground, and the prisoners had only one or two blankets and no extra clothing to ward off the winter chill. And, for the first time in our lives, those of us confined to the "bull pen" experienced a life and death struggle for survival, the unbearable pain from our unattended and infected wounds, and the penetrating December cold of Tule Lake, a God Forsaken concentration camp lying near the Oregon border, and I shall never forget that horrible experience.
Temporary holding facilities for rebellious workers trying to organize into unions were referred to as bullpens. These military prisons were sometimes literally pens normally used for cattle which were pressed into service by stringing barbed wire, establishing a guarded perimeter, and keeping large numbers of men confined in the enclosed space. These "bullpens" have been considered early versions of concentration camps, and were used by the national guard during the Colorado Labor Wars of 1903-04, and in Idaho in 1892 and 1899 during union miners' uprisings near Coeur d'Alene. Author Emma Langdon described these as the first use of the bullpen in the West.
In his autobiography Bill Haywood described Idaho miners held for,
...months of imprisonment in the bull-pen, a structure unfit to house cattle, enclosed in a high barbed-wire fence.
Penned up in bullpens as a response to violence, many hundreds of union men had been imprisoned without trial. Peter Carlson wrote in his book Roughneck,
Haywood traveled to the town of Mullan, where he met a man who had escaped from the bullpen. The makeshift prison was an old grain warehouse that reeked of excrement and crawled with vermin. Overcrowding was so severe that some two hundred prisoners had been removed from the warehouse and quartered in railroad boxcars.
Charlie Siringo described the bull pen as
"...a large stockade with a frame building in the center, for them to sleep and eat in."
In most major league stadiums, the bullpens are located out-of-play just behind the outfield fences. Commonly, the bullpens are separated from each other and each team's is located on the side of the field corresponding with the same team's dugout. However, there are exceptions. In a few ballparks, the team's bullpens are opposite their own dugouts which allows the manager to more easily watch the pitchers warming up from his dugout. A recent trend is the installation of mesh outfield walls in front of the bullpen to allow the bullpen to be more-easily seen by both fans and the manager in the dugout, as well as to allow the players in the bullpen to more easily see what is occurring on the field.
Two major league stadiums currently have their bullpens in foul territory: RingCentral Coliseum (Oakland Athletics) and Tropicana Field (Tampa Bay Rays). This was more common in the past and most new stadiums have opted to move the bullpens to the outfield where the ongoing play is less likely to interfere with the bullpen. In parks with foul-territory bullpens, the relief pitchers and bullpen staff generally sit in chairs or benches along the wall between the field and the stands. The bullpen pitching area is in foul territory and in some of the stadiums, is right up against the foul line. It is therefore not uncommon for batted balls to head towards the bullpen requiring pitchers warming up (and even those sitting along the wall) to move to avoid interfering with a live play or being hit by the ball. There is commonly a ballboy at the end of the bullpen nearest to home plate to attempt to protect the players from foul balls hit in that direction.
Certain ballparks have their outfield bullpens in unusual configurations. Petco Park features the home bullpen behind the outfield fence and the visitor's bullpen behind that and one level higher. The visitor's bullpen was moved to this location from foul territory after the 2012 season.
Between 1950 and 1995, varying numbers of MLB teams used vehicles to transport pitchers from the bullpen to the mound. These bullpen cars ranged from golf carts to full-sized cars. The 1950 Cleveland Indians were the first to use a bullpen car. The last use of a bullpen vehicle was a motorcycle and sidecar used by the Milwaukee Brewers in 1995. However, the Arizona Diamondbacks and the Washington Nationals have since given relief pitchers the option of utilizing a bullpen cart in the 2018 season.
Other current uses of the term include: