An accrued season in football is a way of tracking a player's time and experience in the NFL, which affects his free agency status. This is in contrast to an accredited season, which also keeps track of experience, but for the purpose of payment, including minimum salaries, in addition to a number of other benefits.
A player has earned an accrued season if he has recorded at least six regular-season games on a team's roster on full pay status. This means having an active spot on the roster or being on injured reserve or the Physically Unable to Perform (PUP) list. Players on a team's practice squad or appearing on the Non-Football Related Injury (NFI) or Commissioner's Exempt lists do not record accrued games or seasons.
After his contract ends, a player's free agency status will be determined by the number of accrued seasons he has. If a player has one or two accrued seasons under his belt, he becomes an exclusive rights free agent. In this case, he must sign with the team he has just played for if they offer him a new contract.
A player with three accrued seasons is a restricted free agent. A restricted free agent can talk to other teams about signing with them, but the old team will be involved to some degree and may prevent the free agent from signing with one of those other teams. Finally, a player that has four accrued seasons or more is an unrestricted free agent. This player is allowed to sign with any team in the league that will take him with nothing owed to the team losing the free agent.