But you also can't have an even number of total interleague series without giving teams extended breaks. Each set of series must have an odd number of interleague series going on at the same time (1,3,5, etc.). If there are 2 interleague series going on, then one team from each league would not be playing (2 interleague, 12 intraleague, and 1 sitting). Since there will be 51 sets of series (an odd number), there must also be an odd number of total interleague series. This is because an odd number times an odd number is always odd. 60, 90, 120 total series do not work. 75, 105, 135 do work. Which actually means we just found a flaw in Bob Costas' system! Cool. You are correct as far as you've taken it. But right now, there are 52 series played by each team each season, not 51. That's 26 weeks times 2 series per week minus 1 series lost during the all star break plus one series gained during the once a year 2 consecutive 2 games series. (Each team plays one 2 game series at home and one on the road). This is the mechanism that the schedulers currently use to keep the home/road series/games equal for each team. These 2 game series will not work so well with interleague play, but doing away with them and replacing them with 1 series creates a whole other set of problems. I think it can be worked out, but it's not going to be the "no-brainer" that some people seem to think it is. Agreed, but you can still look at the season as a set of 51 series. It's just that one of those series is actually 2 sets of 2-game series, if that makes sense. While some teams are playing the 2-and-2 series, other teams can be playing a regular 3-game interleague series. Not everybody has to play the 2-and-2 series at the same time. Bob Costas' system has each team playing 8 4-game series and 8 2-game series. All 4-game and 2-game series are played inside the division in his system.