Free agency
An offer sheet is the contract another team gets a restricted free agent to sign, hoping to pry him loose. It starts a short clock: his current team has a couple of days to match the exact terms and keep him, or let him go.
Teams sometimes load an offer sheet with tricky salary structure to make matching as painful as possible. It is free agency's version of a dare.
See it live: pick any team and tap the numbers on its cap sheet.