considered official; four-and-a-half innings are enough if the home team is ahead. Previously, curfews and the absence of adequate lighting caused more ties and shortened games—now, games interrupted from ending in such circumstances are, at least initially, suspended. Also, with more modern playing surfaces better able to handle light rains, the process for calling or shortening a game due to weather has changed; it is more common than in the past to delay a game as much as two hours before a cancellation; also, a delay usually does not occur anymore until the rain is moderate-to-heavy and/or there is standing water on some part of the playing field. In Japan's Nippon Professional Baseball, if the score remains tied after nine innings, up to three extra innings may be played (6 in the playoffs) before the game is called a tie. Since 2011 only regular season games have a 3-hour, 30-minute time limit. Some youth or amateur leagues will end a game early if one team is ahead by ten or more runs, a practice officially known as the "runs ahead rule" (sometimes referred to as a "mercy rule" or "slaughter rule"). Rarely, a game can also be won or lost by forfeit. There is a short break between each half-inning during which the new defensive team takes the field and the pitcher warms up. An existing pitcher is permitted five warm-up pitches and a new pitcher is permitted eight warm-up pitches. The starting pitcher is permitted eight warm-up pitches to begin the game. Traditionally, the break between the top half and the bottom half of the seventh inning is known as the seventh-inning stretch. During the "stretch", fans in the United States often sing the chorus of Take Me Out to the Ball Game. However, since the September 11, 2001 attacks, God Bless America has often been added to it, especially at games in New York City and Washington, D.C., as well as during the All-Star Game and the postseason. In Atlanta and Baltimore it has been a tradition since 1974 to play "Thank God I'm A Country Boy" after "Take Me Out To The Ballgame" during the seventh-inning stretch. At Boston's Fenway Park, a tradition has brought the singing of "Sweet Caroline" in the middle of the eighth inning. Substitutions Each team is allowed to substitute for any player at any time the ball is dead. A batter who