In North American sports contracts, waivers is a type of player transaction. A player under contract to a team is placed on "waivers" for a specified period of time; during this time other teams may submit a claim for that player's contract. Based on a priority system, the team with the highest priority earns either the right to negotiate with the player's current team, or in some cases, the right to assume the contract of that player from the current team. Each of the four major league sports has somewhat different procedures for handling waivers. The purpose of waivers is to prevent teams from colluding to exchange players outside of the normal trade rules, as well as to encourage parity by giving lower-ranked teams the right of first refusal to claim players who are no longer wanted by their former club.