The NBA has its free agency period starting in June during which players whose contracts have run out with their former teams are free to sign with whomever they choose – this is called unrestricted free agency. There can be restricted free agents, as well, whose prior teams have the right to match any offer made to them in the open market and keep them on the roster for the future. NBA teams must stay within a certain range, below the salary cap but above a minimum, for contracts. This amount fluctuates every year depending on earnings by team owners.
Beginner's Guides
Beginner's Guide: How Soccer Works
Beginner's Guide to How the NBA Works
Beginner's Guide on How the NFL Works