An early spring ritual enters its first full week as America’s top college basketball teams face off at four regional sites in the NCAA men’s basketball tournament. If you need added proof that it's a Big Deal to many fans, consider this: A company's contest offers $1 billion to anyone who picks the winner of all 67 games. And for the sixth year, President Obama went on ESPN to fill out a grid -- called a bracket – showing his picks. "I've got Michigan State going all the way," says the fan-in-chief.

Eliminations began last Thursday and now head toward the Sweet Sixteen and Elite Eight rounds this Thursday through Sunday in New York City, Indianapolis, Memphis and Anaheim, Calif. Those regional games set the stage for the Final Four semifinals April 5 in Arlington, Texas, and the championship game there two days later. Every game is televised on either CBS, TBS, TNT or truTV – plus online streaming.

Excitement flows from rooting for local or home state teams, or schools attended by friends or family members. Interest also is generated by the live-action drama of underdog triumphs and long-shot victories at the final buzzer. With more than two weeks of play, a David-beats-Goliath surprise happens most years. On the first day last week, for instance, Harvard won its second NCAA tournament game ever with a 61-57 upset over favored Cincinnati. Off the court, the tournament is a big business -- generating more than 95 percent of the NCAA's revenue from broadcast rights, a share of ticket fees, sponsorships and merchandise sales.

Player says: "Once the ball goes up, anything can happen. Anybody can beat anybody." – Scottie Wilbekin, University of Florida senior

President says: "Michigan State, bring it home for me. It's been a while since I've won my pool."

Broadcaster says: "I equate March Madness to the Olympics. The vast majority of people don't watch college basketball until the tournament. The same as the Olympics." – Greg Anthony, CBS Sports lead analyst