In fantasy football, the waiver wire is how managers add free agents — players not currently on any team in the league. When a player is dropped by another manager, or when a free agent breaks out with a big game, that player typically spends a short period 'on waivers' before anyone can pick him up. During that window, any manager can submit a claim for the player, and the league's rules decide who wins the claim.
The most common method is a rolling priority list or a standings-based order, where teams lower in the standings pick first. Many leagues use FAAB (Free Agent Acquisition Budget) instead, where managers bid fake dollars on players and the highest bid wins. Whoever wins a waiver claim usually moves to the back of the priority list, which keeps one team from hoarding every top free agent.
Using the waiver wire well is one of the most important skills in fantasy football. Finding a backup running back who takes over for an injured starter, or a wide receiver emerging midseason, can turn an average team into a contender. Most leagues open waivers early in the week, often Tuesday or Wednesday morning, after the previous week's games are final.