The NCAA Tournament field is here, and everyone has an opinion about it. How did Oklahoma, Syracuse, and 15-loss Alabama get in? How did Michigan State only get a three seed, Arizona only get a four seed, and Kentucky only get a five seed? The field and seeding conversations will likely end soon, though, as action begins with the First Four play-in games on Tuesday night. 

March Madness is a huge revenue-generator for the NCAA. The college athletics governing body will receive $857 million in broadcast rights alone from Turner this year. 

The tournament is also a favorite annual event for gamblers. So how much will people wager this year? An estimated $10 billion, according to ESPN's David Perdum, who on Monday publicized estimates from the American Gaming Association. 

The catch, of course, is that only an estimated 3 percent is expected to be wagered legally; most of this gambling will happen under the table. Americans spent $2.6 billion on entry fees for tournament pools in 2017, according to Perdum's report.

Nearly 25 percent of United States adults take part in some sort of bracket challenge, many of which are run through workplaces. Market research indicated 63 percent of participants do it to "make it more fun to watch sports and follow the teams and players that you like."

The U.S. Supreme Court is currently reviewing the ban on state-sponsored sports gambling. The forward-thinking NBA is trying to get in on the action. Commissioner Adam Silver and company released their legalized sports gambling plan in January. The NBA wants 1 percent of every bet made on its games. Many, however, are dubious about whether that would ever happen, and whether leagues will end up getting any cut of the profits at all.