In sports, parity is when participating teams have roughly equivalent levels of talent. In such a league, the "best" team is not significantly better than the "worst" team. This leads to more competitive contests where the winner cannot be easily predicted in advance. The opposite condition, which could be considered "disparity" between teams, is a condition where the elite teams are so much more talented that the lesser teams are hopelessly outmatched.
Different major governing organizations attempt to achieve parity in different ways. For example, the NFL in America has established the shared revenue plan, in which all teams equally benefit from television revenue and sales of NFL franchised goods.
Many consider the NFL to be the most "fair" or competitive league, with many different teams having a chance to win each year. In the NFL, complete parity would be a state where on any given Sunday, any given team can win any given game. The illusion of parity in the NFL may be somewhat of a misconception, given that several teams such as the New England Patriots, Pittsburgh Steelers, Indianapolis Colts, and Philadelphia Eagles have appeared in the playoffs in almost all of the past ten years, while a team such as the Buffalo Bills has a playoff drought that is currently over a decade long. Then again, others would say that statistically you could expect some of that variation even in a parity league. Just the same way that you flip a coin ten times in a row, sometimes heads will come up ten times, doesn't mean it's not a fair coin. The most important thing to remember is that a franchise can be struggling and the reason for it can be due to the team's ineptitude when it comes evaluating talent, coaching strategies, developing players, having a good organizational structure, and overall team and player operations.
An example of disparity in sports is Portuguese Liga, the top-flight professional football (soccer) league in Portugal, where three clubs have accounted for 75 of the 77 championships in league history.
Salary cap limits set a maximum amount of money that may be spent on athletes' contracts. These limits exist to different extents in several other leagues as well. For example, Major League Baseball in America does not have a cap, but charges a luxury tax beyond a certain level.