From BR Bullpen
Instant replay was introduced by Major League Baseball on August 28, 2008. MLB became the last of the four major North American sports leagues to use instant replay, mostly over the objections of baseball purists and commissioner Bud Selig, who believe that replays break the longstanding tradition of putting each game's fate in the hands of the umpires on the field. Others object to replays lenghtening an already long game.
The instant replay only applies to home run calls in three situations:
- to determine whether the ball is fair or foul;
- to determine if the ball has left the playing field;
- to determine if the home run was subject to fan interference.
The decision to ask for instant replay to be used is made by the umpire crew chief, who can also decide if a call should be reversed.
Every Major League ballpark now has a television monitor and a secure telephone link to MLB headquarters in New York, where every game being played is monitored by an expert technician and either an umpire supervisor or a former umpire. Should the crew chief at the ballpark decide to ask for the instant replay to be used, he calls the technician in New York who transmits the appropriate footage to the crew chief and umpire crew (the umpire supervisor or former umpire at MLB headquarters is not in direct communication with any of the umpires at the ballpark).
The crew chief must have clear and convincing evidence that the call made by the umpire on the field was incorrect, and the decision to reverse the call rests solely with the crew chief. Once the instant replay has been used, the decision is final; neither team is allowed to argue the decision taken by the crew chief to either reverse the call made on field, or to let it stand.
Should a home run call be reversed, the crew chief then decides on the placement of the baserunners.
Further to their advertising deal with MLB during the 2008 season, all monitors used for the instant replay are SHARP Aquos models. []
 First use of the instant replay
The first MLB instant replay was used after a hit by Yankee Alex Rodriguez during a game on September 3, 2008 at Tropicana Field. The hit was initially ruled to be a home run by third base umpire Brian Runge, but the manager and catcher from the Tampa Bay Rays argued that the ball was foul and asked for a review. After a discussion among the umpires, the crew chief allowed the replay to take place, and the home run call was upheld.
 First reversed home run call
The first 13 reviews all showed correct home run calls. On May 13, 2009, the first homer was overturned. Lance Barksdale ruled a Adam LaRoche hit a home run but on replay, it was found to be a double. LaRoche said he agreed with the ruling.
 First use in the World Series
In Game 3 of the 2009 World Series, on October 31, 2009, Alex Rodriguez hit a high fly ball to the right field corner of Citizens Bank Park in Philadelphia which appeared to hit the top of the fence. Umpire Jeff Nelson originally ruled a double, but New York Yankees manager Joe Girardi came out to argue the call and urge the umpires to review the video evidence. When they did so, it became clear that the ball had in fact hit the lens of a television camera in the first row of the stands; Rodriguez was granted a two-run home run.
 Further use of Instant replay
With the renewal of the Collective Bargaining Agreement after the 2011 season, Major League Baseball sought to extend the use of instant replay to additional situations, namely:
- whether a ball hit down the foul line is fair or foul;
- whether a fly ball was caught or trapped; and
- whether fan interference occurred anywhere on the field.
This came as a result of several controversial calls since the introduction of instant replay on home run calls, particularly in the 2009 Postseason. However, MLB was unable to reach an agreement with the Players' Union and the World Umpires Association prior to the start of the 2012 season, and adoption of these additional uses was postponed until 2013. Among the issues at play were the uneven number of camera angles available in different ballparks and disagreements on how to implement the additional possibilities for review in a way that is least disruptive to the flow of the game. On July 27, 2012, Commissioner Selig confirmed that there was now agreement for expansion of instant replay in the first two of these areas in 2013.
On August 15, 2013, Selig announced plans to expand review even further, by allowing each manager up to three challenges per game - one to be used in the first six innings and two for the last three innings. These challenges would only be used for "reviewable" calls, which manager will not otherwise be allowed to argue; a number of umpires' decisions will remain "un-reviewable". The exact list of which types of call are reviewable and which are not still needs to be specified. before being implemented, the proposal will need to be formerly approved by Major League owners at the 2013 winter meetings and receive the approval of the Players Union and Umpires Association, in order to come into effect for the 2014 season.