Thursday is something of a national holiday for American sports fans, when office productivity plummets. The NCAA Men's Division I Basketball Championship, also known as March Madness or the Big Dance, begins in earnest. Thursday and Friday feature a hoops 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 underdogs trying to spark an improbable run and become the next tournament darling. Fanatics, novices and even President Barack Obama are trying to predict the winners of every game by completing an estimated 70 million tournament brackets, according to the American Gaming Association - that's more brackets completed than votes Obama received in the last presidential election. Here's a brief explanation of how a basketball tournament transcended sports to become a national craze:
DAVID VERSUS GOLIATH
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 first NCAA Tournament, which featured only eight teams. The NCAA field kept growing as TV coverage spurred interest. 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. The classic game 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. The term ''March Madness'' was popularized through the 1980s as unlikely champions such as 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. Every game is now 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 - had up until the moment the first game tipped shortly after noon Eastern (1600 GMT) Thursday. Some use advanced stats, others pick based on mascots - could a Mountaineer (West Virginia) tame a Bull (Buffalo)? 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.