The NFL combine is a four day event designed as a showcase of collegiate talent for the upcoming NFL Draft. Started in 1977, potential draft picks are invited to the special camp where they prodded, poked, drilled, and tested, all to give NFL teams a better indication of who they'll select in the April draft. Since 1988, only three players who did not participate in the combine were drafted in the first round, so it's important for the players who are invited to show up.
Upon arriving at the combine, players are separated by position and sent to different stations for physical measurements and a strength test in the form of a 225-pound bench press - the more reps, the better. The players then take the Wunderlic intelligence test, and record two interviews that will later be sent to all 32 NFL teams.
The next part of the combine are the team meetings, in which players meet with specific teams for interviews and psychological tests. If a team has a high draft pick, they may meet with as many as fifty players on the first day. A team near the bottom of the draft will likely skip interviews with the potential number ones.
The following day players will be measured in 40-yard dashes, vertical leaps, and position-specific football drills, like blocking, route-running, and passing accuracy. At the same time a different group of players will be rotating through the first day's events.
The skills demonstrated during this four day period can move players from a third or fourth round pick into the first round, which equates to a difference of several million dollars. At the same time, teams must be weary about selecting players based on their combine performance. The Bears selected Brian Urlacher based on his incredible performance in the combine. Urlacher has so far turned out to be one of the best middle linebackers in the NFL. By the same token, however, the Eagles selected Mike Mamula in the first round based on combine scores, and five years later he's retired from pro football. | 
