The Magic Number and September Baseball... they go together like peanut butter and ladies.
"We go together like cocaine and waffles and alimony!"
The Magic Number, of course, is a figure that represents the total number of first place team wins combined with second place team losses that would clinch the division/wild card for that particular team. When a team's magic number reaches 1 they are guaranteed at least a tie in their division/wild card.
For example, the Cleveland Indians enter play tonight with a Magic Number of 20. Any combination over the next 3 1/2 weeks of baseball of Indians wins and Tigers losses that add up to 20 will clinch the A.L. Central for the Tribe.
But have you ever wondered how those folks in the sports media ivory towers come up with the mythical Magic Number? It's actually remarkably easy to calculate. All you need to do is take 162 (the number of games in the MLB season) add 1 (to eliminate a tie in the division/wild card), then subtract the number of wins the first place team has (W1st) and subtract the number of losses the second place team has (L2nd) to arrive at the Magic Number.
The formula looks like this:
MN = 163 - W1st - L2nd
I'll use the example of the Indians again. They enter play tonight at 79-58 while the Tigers are 73-64; each have played 137 games with 25 remaining with the Tribe holding a 6-game lead. The formula reads: 163 - 79 - 64 = 20. The math adds up as if the Indians, with their 6-game lead, win 20 of their remaining 25 games, it is impossible for Detroit to win the A.L. Central.
The more advanced explanation of the mathematics involved can be found at the Obsolete Computer Museum.
You can also use the Magic Number formula to check if teams are eliminated. Teams such as the Devil Rays (the second hottest team in the bigs right now, thankyouverymuch), whose number of losses we will substitute for L2nd: 163 - 83 - 81 = -1... so, sadly, the Red Sox' win on Sunday nixed the Rays' hopes of their first ever A.L. East title. You can also use this formula to check a second place team's Magic Number.
The more you know.