When free agency starts, all teams must be in compliance with the league's salary cap. This year it's $155,270,000. That, of course, determines a lot about the kind of spending each team does during the period.
Free agents are players who are not under contract to any team. Some players have already reached agreements with teams, like defensive end
There are two kinds of free agents -- unrestricted and restricted.
Unrestricted free agents have completed four or more accrued seasons with a team and are allowed to sign with any club through July 22 (or the first scheduled day of the first NFL training camp).
Restricted free agents have been with their teams for three accrued seasons and have received a qualifying offer (a salary tender predetermined by the Collective Bargaining Agreement) from their current clubs.
This group of players can negotiate with any team through April 22. If a restricted free agent receives and signs an offer sheet from a new club, his old team can either retain him by matching the offer or let him go and possibly receive draft choice compensation.
Both kinds of free agents can be tagged by their old teams as an exclusive franchise player, a non-exclusive franchise player or a transition player. Clubs can use the franchise tag -- either exclusive or non-exclusive -- and the transition tag once a season.
A player who receives the exclusive or non-exclusive tag is tendered a one-year contract based on the top five salaries at his position. Exclusive players can't negotiate with other teams, while non-exclusive players can. A team that signs a non-exclusive player has to compensate the old club with two first-round draft picks.