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Effect of Astros joining AL on scheduling
Starting in 2013, the Houston Astros will join the American League, giving each league 15 teams. This will force interleague play throughout the season. For the first time ever, teams will play interleague games even on opening day and during key division races all the way to the end of the season. This does not require expanding the number of interleague games because currently the number of interleague games is 252/2430 or about 1 in 9.6 games (not an integer because not all teams have the same number of interleague games). With an odd number of teams in each league, one teams in each league would be the "odd man out" and have to play an interleague game to fill out the schedule, meaning as few as 1 in 15 games could be interleague (14 AL teams in 7 AL games, 14 NL teams in 7 NL games and 1 AL and 1 NL team in an interleague game). Despite this, there have been proposals to increase interleague play anyway, to 30 games[13]. While the increase to 30 games is unlikely for the first few years of the same number of teams in each league, a smaller increase could take place immediately. One such proposal is for every team to play 20 interleague games.[14]. This would be done by having every team from one division play a 3 game series against four of the five teams another division of the other league on a rotating 3 year cycle. Every team would also play the fifth team from the same division of the other interleague games four times in either one four game series or two-two game series. The final four games would be rivalry games (such as Yankees-Mets, White Sox-Cubs, etc) played in two sets of two game series, one series a piece at home. However doing so would result in teams playing different amounts of home and away interleague games (8 home and 12 away or vice versa). While interleague play will be required every day, it is undesirable to have it early or late in the season. To remedy this, there will only be one interleague series in the first and last five weeks of the season, and no team will have to play more than one road series (to minimize playing by the other leagues rules) during this time. In addition, since the Astros would have to start using a designated hitter full-time, there is debate within MLB to unify the rules of the two leagues, with either the NL adopting the DH or the AL returning to its pre-1973 rules and have the pitcher hit, like the NL