Bird rights are a salary cap exception allowing a team to re-sign its own free agent for any amount up to the maximum, even if the team is over the cap.
Bird rights are the exception that built dynasties. Named for Larry Bird, whose situation prompted the rule in the 1980s, they let a team exceed the cap to re-sign its own player once that player has spent three seasons with the team without being waived or changing teams as a free agent. Shorter stays produce weaker versions, Early Bird rights after two seasons and Non-Bird rights after one, each with its own raise limits.
The strategic consequences fill transaction season. Teams plan summers around Bird rights math, signing outside players with cap space first and re-signing their own stars last, above the cap, and a player's Bird rights travel with him in a trade, which makes expiring contracts of good players so valuable to acquiring teams.
The rule exists to reward continuity: without it, the cap would force contenders to let their own cores leave, and the league decided in the Bird era that fans keeping their stars was worth a loophole. Quiz questions about famous re-signings and impossibly expensive rosters usually resolve to this term, the legal mechanism by which a payroll climbs far past the cap without breaking a single rule.
In use"Keeping his Bird rights meant they could re-sign him last and spend their cap space first."