March Madness explained: When America goes basketball mad

Thursday marks something of a national holiday for American sports fans, when office productivity plummets. The NCAA Men's Division I Basketball Championship, better known as March Madness or the Big Dance, begins in earnest. A few play-in games have already happened, but Thursday and Friday feature the real opening extravaganza: 16 games each day, from noon to midnight. The single-elimination tournament means every game is a must-win for all 68 schools, producing tense, dramatic finishes. Upsets are eagerly anticipated as elites like Kentucky fend off unknowns trying to spark an improbable run and become the next tournament darling, like last year's Dayton. Fanatics, novices and even President Barack Obama are trying to predict the winners of every game of every round by completing an estimated 70 million tournament brackets, according to the American Gaming Association — that's more brackets completed than votes cast in the last presidential election. Here's a brief explanation of how a basketball tournament transcended sports to become a national craze:

Madness from the start

College basketball has long filled the gap in the American sports calendar when baseball and football are dormant. In 1939, Oregon beat Ohio State in the inaugural eight-team tournament. It seems modest now, but it was a risky venture: a year earlier the rival National Invitational Tournament had begun at New York's old Madison Square Garden, already the most famous venue in basketball. The two tournaments competed for years, before the NCAA, as college sports' governing body, managed to force member schools to participate in its tournament if they were invited (the NIT still exists as a consolation tournament). The NCAA field kept growing as TV coverage spurred interest, so more spots were given to smaller schools. The potential for a David to slay a Goliath set the stage for what remains the most-watched basketball game ever: the 1979 final pitting little-known Indiana State, led by Larry Bird, against powerhouse Michigan State, led by Magic Johnson. A quarter of U.S. homes tuned in for the classic game that transformed Bird and Johnson into rival superstars and catapulted college basketball into the American consciousness.

The big dance gets bigger

The fledgling ESPN cable network began broadcasting the tournament's oft-ignored early rounds in 1980, giving national exposure to lesser-known schools. CBS popularized the term "March Madness" through the 1980s as unlikely champions like North Carolina State and Villanova captivated Americans. TV ratings skyrocketed, and so did revenue for the NCAA. In 2013, according to the latest figures available from Kantar Media, TV advertising revenue was a staggering $1.15 billion, more than even the NFL playoffs and Super Bowl (though pro football, by far the most popular American sport, has far fewer postseason games). This year, 68 schools play in 14 venues across the U.S. Every game will be on TV and streaming online. The champion must win six games as the field winnows, from the Sweet 16 to the Elite Eight to the Final Four. The semifinals and championship will be played April 4-6 in a football stadium in Indianapolis.

An American Obsession: Brackets! Upsets!

Fans competing in online bracket pools — often for money, though that's technically illegal — have up until the moment the first game tips shortly after noon Eastern (0400 GMT) Thursday. Brackets will be busted by unpredictable upsets, like tiny Mercer's dethroning of Duke last year. One of the most famous upsets was achieved in 2001 by Hampton. Who does Kentucky, this tournament's overwhelming favorite, play in its first game? Hampton. That game just happens to be scheduled for prime-time on Friday night. Kentucky is favored to win by 32 points, according to oddsmakers. But in March, anything is possible.