Monday was the 29th anniversary of one of the most famous moments in sports gambling history: "Black Sunday," or the unfortunate outcome of Super Bowl XIII for bookmakers. As this 2005 USA Today story explained:

"Bookmakers [in Las Vegas] still wince when they talk about so-called "Black Sunday," otherwise known as Super Bowl XIII between the Pittsburgh Steelers and the Dallas Cowboys in 1979. The week before the game, Pittsburgh was installed as the four-point favorite. The line fluctuated between 3½ and 4½ before finally settling at four.

"Pittsburgh beat Dallas 35-31. And every sports book in Vegas took the hit."

In short, the movement of the pointspread set up a prime "middling" opportunity. Bettors could take Pittsburgh at 3½ and Dallas at 4½ and cash both tickets if the game fell on four. What's more, the bettors who made bets at Pittsburgh -4 and Dallas +4 got their money back. 

Bettors could conceivably "middle" Super Bowl XLI if they were to have bet the Giants plus-14 on Sunday night and the Patriots minus-12 in the last couple of days and hope for the game to the Patriots to win by 13. But I doubt the sports books are too worried about that prospect.