8 Schools have entered the tournament ranked #1 in at least one of the three polls. This has happened 21 times by those 8 teams which are.
In 2006, the third seeded (in the Minneapolis bracket) University of Florida gators defeated the #2 seeded UCLA (in the Oakland bracket) in the national championship. Neither team was a number one seeed
usually by their records and previous tournament performances
Villanova
The higher seed is considered the home team
Michigan was a #3 seed when they won the NCAA Men's Basketball Tournament in 1989.
You have the advantage, or you may be seeded higher in a tournament.
Kansas was the #6 seed in the Midwest bracket in 1988.
What rank the player is in the world or most likely the tournament. This is chosen by how good their world ranking is. They also take into account past performance, as well as how good the player is on the surface - e.g. in 2005, Andy Roddick was ranked lower than Lleyton Hewitt, but he was seeded 2nd ahead of Hewitt (Federer was obviously seeded first), due to his success at the tournament the previous year (reached the final), and his success on the grass courts at Queens. Seeded players earn a 'seed number' by having a high ranking/good record. The seed 'number' is awarded based on the expectation (usually based on rankings) which indicate how the player might perform in this tournament. The 1 seed would be expected to win the tournament and is usually the highest ranked of all the players in the tournament. The number of seeds in a tournament depends on the number of competitors.
16 seeded Harvard defeated 1 seed Stanford in the 1998 women's NCAA tournament. That is the only victory by a 16 seed in either the men's or women's tournament.
#1 seeded Kansas defeated Kentucky in the second round of the 2007 NCAA Tournament, by a score of 88-76.
16 seed, beat duke last year
The lowest seeded team to make it all the way to the Final Four in the NCAA basketball tournament was an 11 seed and it happened four times:11 seeded LSU in 198611 seeded George Mason in 200611 seeded VCU in 201111 seeded Wichita State in 2013