When a player's contract is up with their current team, he becomes a free agent. This means that during the offseason, the player will have the opportunity to field contract offers from other teams and potentially sign with a new team. Based on the terms set forth in their recently expired contracts, however, some players have restrictions on who they can sign with while other players are free to go wherever they please.
Restricted free agents are players with an expiring contract that have played in the NFL for three or fewer seasons. Restricted free agents are permitted to field new contract offers from other teams, but once an offer is accepted, their current team has a chance to match the offer. If the player's current team elects to match the offer the player has agreed to from another team, the current team automatically gets to keep the player for the same length of time and yearly salary.
Unrestricted free agents are players with an expiring contract that have played in the NFL for three or more seasons. Unrestricted free agents have no obligation to their former team and are free to leave for a new team once they agree upon a suitable contract offer.