"I believe that the extraordinary technology that we now have merits the use of instant replay on a very limited basis," commissioner Bud Selig said. "The system we have in place will ensure that the proper call is made on home run balls and will not cause a significant delay to the game."
Three series are scheduled to start Thursday, with Philadelphia at the Chicago Cubs, Minnesota at Oakland and Texas at the Los Angeles Angels. For other games, replays will be available to umpires starting Friday.
For now, video will be used only on so-called "boundary calls," such as determining whether fly balls went over the fence, whether potential home runs were fair or foul and whether there was fan interference on potential home runs.
Selig, who opposed replay in the past, said he won't allow its use to expand to additional types of calls.
" My opposition to unlimited instant replay is still very much in play," Selig said. "I really think that the game has prospered for well over a century now doing things the way we did it."
Video from all broadcast feeds will be collected at the office of Major League Baseball Advanced Media in New York, where it will be monitored by a technician and either an umpire supervisor or a retired umpire. If the crew chief at a game decides replay needs to be checked, umpires will leave the field, technicians at MLBAM will show umpires the video and the crew chief will make the call, overturning the original decision only if there is "clear and convincing evidence."
Leaving the dugout to argue a call following a replay will result in an automatic ejection.
Selig said the use of replays may shorten games because it might eliminate some arguments.
"While the use of instant replay is an experiment, we hope that over the balance of this season it will prove to be a success," players' union head Donald Fehr said.
The players' association agreed to replay for the balance of the season but retained the right, through Dec. 10, to ask for additional bargaining for future years. If players don't, the replay agreement will run through 2011.
Baseball had been the last holdout among the major professional sports in the United States. Replays were first used in the NFL in 1986.
In the NHL, video review has been in place since the 1991-92 season to check whether the puck crossed the goal line completely, went in before time expired or the net was dislodged, and wasn't kicked or batted in intentionally.
In the NBA, replays have been viewed since the 2002-3 season to decide whether players got off shots before time expired and since last season to aid decisions following altercations and flagrant fouls. In grand slam tennis tournaments, a Hawk-Eye system has been used to decide close line calls since the 2006 U.S. Open.
International soccer has refused to embrace aiding referees, with FIFA's International Football Association Board voting last March to stop all experiments with technology that could determine whether balls cross goal lines.